View source for Engineering:SD card

{{Short description|Type of memory storage for portable devices}}
{{Infobox storage medium
| name = Secure Digital<br/>(SD, SDHC, SDXC, SDUC)
| logo = SD-Logo.svg
| image = SD Cards.svg
| caption = From top to bottom: SD, miniSD, microSD
| type = [[Memory card]]
| capacity = {{Unbulleted list
 | '''SD''': Up to {{Nowrap|2 GB}}
 | '''SDHC''': {{Nowrap|over 2 GB}} to {{Nowrap|32 GB}}
 | '''SDXC''': {{Nowrap|over 32 GB}} to {{Nowrap|2 TB}}
 | '''SDUC''': {{Nowrap|over 2 TB}} to {{Nowrap|128 TB}}
 }}
| blocksize = Variable
| read = {{Unbulleted list
 | '''Standard''': 12.5 MB/s
 | '''High-speed''': 25 MB/s
 | '''UHS-I''': 50 MB/s or 104 MB/s
 | '''UHS-II''': 156 MB/s full-duplex, or 312 MB/s half-duplex
 | '''UHS-III''': 312 MB/s full-duplex, or 624 MB/s half-duplex
 | '''Express''': {{Nowrap|≥ 985 MB/s}} full-duplex
 }}
| write = Variable
| standard = SD Standard
| owner = [[Organization:SD Association|SD Association]]
| use = Portable devices, such as digital cameras and mobile phones (including most smartphones)
| dimensions = {{Unbulleted list
 | '''Standard''':
 | {{cvt|32.0|*|24.0|*|2.1|mm}}<br>{{cvt|1612.8|mm3}}
 | '''Mini''':
 | {{cvt|21.5|*|20.0|*|1.4|mm}}<br>{{cvt|602|mm3}}
 | '''Micro''':
 | {{cvt|15.0|*|11.0|*|1.0|mm}}<br>{{cvt|165|mm3}}
 }}
| weight = {{Unbulleted list
 | '''Standard''': {{Nowrap|~2 [[Gram|g]]}}
 | '''Mini''': {{Nowrap|~800 mg}}
 | '''Micro''': {{Nowrap|~250 mg}}
 }}
| extended from = MultiMediaCard
| extended to = 
| released = August 1999
| discontinued = 
}}

'''Secure Digital''', officially abbreviated as '''SD''', is a [[Engineering:Proprietary hardware|proprietary]], [[Non-volatile memory|non-volatile]], [[Flash memory|flash]] [[Memory card|memory card]] format the [[Organization:SD Association|SD Association]] (SDA) developed for use in portable devices.

The standard was introduced in August 1999 by [[Company:SanDisk|SanDisk]], [[Company:Panasonic|Panasonic]] (Matsushita) and [[Company:Toshiba|Toshiba]] as an improvement on MultiMediaCards (MMCs).<ref name="partnership">{{cite web|title=Matsushita Electric, SanDisk and Toshiba Agree to Join Forces to Develop and Promote Next Generation Secure Memory Card|publisher=DP Review |url=http://www.dpreview.com/articles/6861681955/newmemory|access-date=2016-02-23|date=1999-08-24}}</ref> SDs have become an industry standard. The three companies formed SD-3C, LLC, a company that licenses and enforces intellectual property (IP) rights associated with SD memory cards and SD host-and-ancillary products.<ref name="SD-3C">{{cite web|title=Welcome to SD-3C, LLC|publisher=SD-3C |url=https://www.sd-3c.com/|access-date=2016-02-23|date=2015-03-30}}</ref>

In January 2000, the companies formed the [[Organization:SD Association|SD Association]] (SDA), a non-profit organization to create and promote SD Card standards.<ref name="SD Association">{{cite web|title=Matsushita Electric, SanDisk and Toshiba to Form SD Association to Promote Next Generation SD Memory Card|publisher=Toshiba |url=https://www.toshiba.co.jp/about/press/2000_01/pr0602.htm|access-date=2016-02-23|date=2015-03-30}}</ref> {{As of|2023}}, the SDA has approximately 1,000 member companies. It uses several SD-3C-owned trademarked logos to enforce compliance with its specifications and denote compatibility.<ref>{{cite web|url=https://www.youtube.com/watch?v=wX6NwBa1csY | archive-url=https://ghostarchive.org/varchive/youtube/20211029/wX6NwBa1csY| archive-date=2021-10-29|title=Using SD Memory Cards is Easy |publisher=SD Association |date=2010-06-22 |access-date=2014-01-02}}{{cbignore}}</ref>


== History ==

=== 1999–2005: Creation and introduction of smaller formats ===
In 1999, [[Company:SanDisk|SanDisk]], [[Company:Panasonic|Panasonic]] (Matsushita) and [[Company:Toshiba|Toshiba]] agreed to develop and market the Secure Digital (SD) memory card.<ref>{{cite web|url=http://www.dpreview.com/articles/6861681955/newmemory|title=Three Giants to develop new "Secure Memory Card" |publisher=DP review|access-date=2016-02-23}}</ref> The card was derived from the MultiMediaCard (MMC) and provided [[Engineering:Digital rights management|digital rights management]] (DRM) based on the [[Social:Secure Digital Music Initiative|Secure Digital Music Initiative]] (SDMI) standard and a high memory density.{{cn|date=September 2023}}

SD was designed to compete with the [[Memory Stick]], a DRM product [[Company:Sony|Sony]] had released the year before. Toshiba hoped its DRM would encourage music suppliers concerned about piracy to use SD cards.<ref>{{cite web|url=http://www.toshiba.co.jp/about/press/2003_07/pr1701.htm|title=Press Releases 17 July 2003|publisher=Toshiba|date=2003-07-17|access-date=2010-08-22}}</ref>

The trademarked SD logo was originally developed for the Super Density Disc, which was the unsuccessful Toshiba entry in the [[Engineering:DVD|DVD]] format war. For this reason, the letter "D" is styled to resemble an optical disc.<ref>{{Citation |title=The Odd History of the SD Logo |url=https://www.youtube.com/watch?v=VeLvdE8lNW4 |access-date=2023-10-25 |language=en}}</ref>

At the 2000 [[Engineering:Consumer Electronics Show|Consumer Electronics Show]] (CES), the three companies announced the creation of the [[Organization:SD Association|SD Association]] (SDA) to promote SD cards. The SD Association, which was headquartered in San Ramon, California, United States, then had 30 member companies and product manufacturers that made interoperable memory cards and devices. Early samples of the SD card<ref>{{cite web|url=https://www.bitwarsoft.com/what-is-an-sd-card.html |title=What is SD Card |publisher=Bitwarsoft.com |date=2020-07-24 |access-date=2021-06-30}}</ref> became available in the first quarter of 2000, and production quantities of 32 and 64 [[Megabyte|megabyte]] (MB){{efn|except where indicated otherwise, 1 MB equals one million bytes}} cards became available three months later.{{cn|date=September 2023}}<!-- found source? <ref>https://www.global.toshiba/ww/news/corporate/2000/01/pr0602.html</ref>--> The first 64MB cards were for sale for 200 USD.<ref>{{Cite web|url=https://books.google.com/books?id=xA5vzkW8IDsC&pg=PA40&dq=64mb+sd+card+second+quarter+2000&hl=en&sa=X&ved=2ahUKEwjqh6ro5fmDAxVwnIQIHbfUB4U4FBDoAXoECAoQAw#v=onepage&q&f=false|title=Popular Science|first=Bonnier|last=Corporation|date=August 27, 2000|publisher=Bonnier Corporation|via=Google Books}}</ref> SD was envisioned as a single memory card format for several kinds of electronic devices, that could also function as an expansion slot for adding new capabilities for a device.<ref>{{Cite web|url=https://books.google.com/books?id=VW7ZIgUJwSMC&pg=PA90&dq=64mb+sd+card+second+quarter+2000&hl=en&sa=X&ved=2ahUKEwjMwZy75fmDAxWtQTABHfXZDmEQ6AF6BAgKEAM#v=onepage&q=64mb+sd+card+second+quarter+2000&f=false|title=Popular Science|first=Bonnier|last=Corporation|date=May 27, 2000|publisher=Bonnier Corporation|via=Google Books}}</ref>

==== miniSD ====
[[File:Huawei_U8950D_no_cover.JPG|thumb|microSD card in a smartphone ]]

At March 2003 CeBIT, SanDisk Corporation introduced, announced and demonstrated the '''miniSD''' form factor.<ref name="miniSD_announcement">[http://www.sandisk.com/Corporate/PressRoom/PressReleases/PressRelease.aspx?ID=1536 SanDisk Introduces The World's Smallest Removable Flash Card For Mobile Phones-The miniSD Card] SanDisk.com</ref> The SDA adopted the miniSD card in 2003 as a small-form-factor extension to the SD card standard. While the new cards were designed for mobile phones, they were usually packaged with a miniSD adapter that provided compatibility with a standard SD memory card slot.{{cn|date=September 2023}}

==== microSD ====
'''MicroSD''' form-factor memory cards were introduced in 2004 and originally called T-Flash,<ref>{{cite news |title=T-Flash: aka 'Yet Another Memory Card Format' |first=Peter |last=Rojas |date=2 March 2004 |journal=[[Software:Engadget|Engadget]] |url=https://www.engadget.com/2004/03/02/t-flash-aka-yet-another-memory-card-format/}}</ref> and later TransFlash, which was abbreviated to "T-Flash" or "TF". TransFlash and microSD cards are functionally identical, allowing either to operate in devices made for the other.<ref name="Phonescoop">{{cite web|url=https://www.phonescoop.com/articles/article.php?a=801 |title=SanDisk Reveals Tiny New Memory Cards for Phones |publisher=Phonescoop.com |date=28 February 2004 |access-date=2014-01-02}}</ref> An adapter allowed the use of MicroSD and TransFlash cards in SD card slots.<ref name="Phonescoop"/>

=== 2006–2008: SDHC and SDIO ===
[[File:8 bytes vs. 8Gbytes.jpg|thumb|This microSDHC card holds 8 billion bytes. Beneath it is a section of a [[Magnetic-core memory|magnetic-core memory]] (used until the 1970s) that holds eight bytes using 64 cores. The card covers approximately 20 bits ({{frac|2|1|2}} bytes).]]

In September 2006, SanDisk announced the 4&nbsp;GB miniSDHC.<ref name="miniSDHC_announcement">[http://www.sandisk.com/Corporate/PressRoom/PressReleases/PressRelease.aspx?ID=3530 SanDisk Introduces 4GB miniSDHC Flash Card for Mobile Phones] SanDisk.com</ref> Like the SD and SDHC, the miniSDHC card has the same form factor as the older miniSD card but the HC card requires HC support built into the host device.{{cn|date=September 2023}} Devices that support miniSDHC work with miniSD and miniSDHC, but devices without specific support for miniSDHC work only with the older miniSD card. Since 2008, miniSD cards are no longer produced, due to market domination of the even smaller microSD cards.{{cn|date=September 2023}}

=== 2009–2019: SDXC ===
[[File:MicroSDXC.64GB.P1127589.jpg|thumb|right|Macro shot of a microSDXC memory card with eight gold plated electrical contacts]]

The storage density of memory cards increased significantly{{quantify|by how much?|date=June 2023}} throughout the 2010s, allowing the earliest devices to offer support for the SD:XC standard, such as the [[Engineering:Samsung Galaxy S III|Samsung Galaxy S III]] and [[Engineering:Samsung Galaxy Note II|Samsung Galaxy Note II]] mobile phones, to expand their available storage to several hundreds of [[Gigabyte|gigabyte]]s.

In January 2009, the SDA announced the SDXC family, which supports cards up to 2&nbsp;TB{{efn|name="here, 1 TB = 1024"|reference=here, 1 TB = 1024<sup>4</sup> B}} and speeds up to 300&nbsp;MB/s.<ref>{{cite web |title=SDXC SIGNALS NEW GENERATION OF REMOVABLE MEMORY WITH UP TO 2 TERABYTES OF STORAGE |url=https://www.sdcard.org/cms/wp-content/uploads/2020/11/SD_Association_Announces_SDXC_Revised_1-7-09.pdf |website=sdcard.org |publisher=SD Association |access-date=30 December 2023}}</ref> SDXC cards are formatted with the [[ExFAT|exFAT]] file system by default.<ref>{{Cite web |date=2020-12-11 |title=Capacity (SD/SDHC/SDXC/SDUC) {{!}} SD Association |url=https://www.sdcard.org/developers/sd-standard-overview/capacity-sd-sdhc-sdxc-sduc/ |access-date=2022-03-08 |website=sdcard.org |language=en-US}}</ref> SDXC was announced at [[Engineering:Consumer Electronics Show|Consumer Electronics Show]] (CES) 2009 (January 7–10). At the same show, [[Company:SanDisk|SanDisk]] and [[Company:Sony|Sony]] also announced a comparable Memory Stick XC variant with the same 2&nbsp;TB{{efn|name="here, 1 TB = 1024"}} maximum as SDXC,<ref>{{cite web| url= http://www.sandisk.com/about-sandisk/press-room/press-releases/2009/2009-01-07-sandisk-and-sony-to-expand-%E2%80%9Cmemory-stick-pro%E2%80%9D-and-%E2%80%9Cmemory-stick-micro%E2%80%9D-formats |title= SanDisk and Sony to expand Memory Stick Pro and Memory Stick Micro formats |publisher=SanDisk |date= 2009-01-07 |access-date=2010-08-22}}</ref> and [[Company:Panasonic|Panasonic]] announced plans to produce 64&nbsp;GB SDXC cards.<ref name="betanews_2t_sdxc">{{cite web |last=Mook |first=Nate |date=2009-01-08 |title=SD Card, Memory Stick formats to reach 2 terabytes, but when? |url=https://betanews.com/2009/01/08/sd-card-memory-stick-formats-to-reach-2-terabytes-but-when |access-date=2024-01-22 |work=Beta news}}</ref> On March 6, Pretec introduced the first SDXC card,<ref name="dpreview pretec sdxc">{{cite web|url= http://www.dpreview.com/news/0903/09030601pretecsdxc.asp | title =Pretec introduces world's first SDXC card | work = Digital Photography Review | date=2009-03-06 |access-date=2010-08-22}}</ref> a 32&nbsp;GB card with a read/write speed of 400&nbsp;Mbit/s. But only early in 2010 did compatible host devices come onto the market, including [[Company:Sony|Sony]]'s Handycam HDR-CX55V [[Engineering:Camcorder|camcorder]], Canon's [[Engineering:Canon EOS 550D|EOS 550D]] (also known as Rebel T2i) Digital SLR camera,<ref name="The-Digital-Picture.com-T2i_500D">{{cite web| title= Canon EOS Rebel T2i/550D Digital SLR Camera Review|url= http://www.the-digital-picture.com/Press-Release/Canon-EOS-Rebel-T2i-550D-Digital-SLR-Camera-Press-Release.aspx | publisher = The Digital Picture}}</ref> a USB card reader from Panasonic, and an integrated SDXC card reader from JMicron.<ref name="JMicron">{{cite web | url = http://www.dailytech.com/Lack+of+Card+Readers+Holding+Back+SDXC+Flash+Memory+Adoption/article16915.htm | title = Lack of Card Readers Holding Back SDXC Flash Memory Adoption | access-date = 2009-12-22 | last = Ng | first = Jansen | date = 2009-11-24 | publisher = DailyTech | archive-date = 2007-06-11 | archive-url = https://web.archive.org/web/20070611074105/http://www.dailytech.com/ | url-status = dead }}</ref> The earliest laptops to integrate SDXC card readers relied on a USB 2.0 bus, which does not have the bandwidth to support SDXC at full speed.<ref name="Laptops">{{cite web | url = http://www.dailytech.com/Lenovo+HP+Dell+Integrating+SDXC+Readers+in+New+32nm+Intel+Arrandale+Laptops/article16937.htm | title = Lenovo, HP, Dell Integrating SDXC Readers in New 32nm Intel "Arrandale" Laptops | access-date = 2009-12-22 | last = Ng | first = Jansen | date = 2009-11-30 | publisher = DailyTech | archive-date = 2015-01-01 | archive-url = https://web.archive.org/web/20150101030411/http://www.dailytech.com/Lenovo+HP+Dell+Integrating+SDXC+Readers+in+New+32nm+Intel+Arrandale+Laptops/article16937.htm | url-status = dead }}</ref>

In early 2010, commercial SDXC cards appeared from [[Company:Toshiba|Toshiba]] (64 GB),<ref name="DailyTech">{{cite web | url = http://www.dailytech.com/Toshiba+Sampling+First+SDXC+Flash+Memory+Cards/article16972.htm | title = Toshiba Sampling First SDXC Flash Memory Cards | access-date = 2009-12-22 | last = Ng | first = Jansen | date = 2009-12-22 | publisher = DailyTech | archive-date = 2010-11-25 | archive-url = https://web.archive.org/web/20101125031137/http://www.dailytech.com/Toshiba+Sampling+First+SDXC+Flash+Memory+Cards/article16972.htm | url-status = dead }}</ref><ref name="CrunchGear">{{cite web | url = http://www.crunchgear.com/2010/04/15/toshibas-64gb-sdxc-card-to-finally-go-on-sale-in-japan/ | title = Toshiba's 64&nbsp;GB SDXC card to finally go on sale (in Japan) | access-date = 2010-08-09 | publisher = CrunchGear | archive-date = 2010-07-01 | archive-url = https://web.archive.org/web/20100701214307/http://www.crunchgear.com/2010/04/15/toshibas-64gb-sdxc-card-to-finally-go-on-sale-in-japan/ | url-status = dead }}</ref> Panasonic (64&nbsp;GB and 48&nbsp;GB),<ref name="Panasonic">{{cite web | url = http://www2.panasonic.com/webapp/wcs/stores/servlet/prModelDetail?storeId=11301&catalogId=13251&itemId=389511&modelNo=Content01052010041118461&surfModel=Content01052010041118461 | title = Panasonic Introduces New 64&nbsp;GB* and 48&nbsp;GB* SDXC Memory Cards, Available Globally in February 2010 | access-date = 2010-08-09 | publisher = [[Company:Panasonic|Panasonic]] | archive-date = 2010-04-21 | archive-url = https://web.archive.org/web/20100421194326/http://www2.panasonic.com/webapp/wcs/stores/servlet/prModelDetail?storeId=11301&catalogId=13251&itemId=389511&modelNo=Content01052010041118461&surfModel=Content01052010041118461 | url-status = dead }}</ref> and SanDisk (64&nbsp;GB).<ref name="SanDisk">{{cite web | date = 2010-02-22 | url = http://sandisk.com/about-sandisk/press-room/press-releases/2010/2010-02-22-sandisk-ships-its-highest-capacity-sd-card-ever,-the-64gb-sandisk-ultra-sdxc-card | title = Sandisk ships its highest capacity sd card ever | access-date = 2010-08-09 | publisher = [[Company:SanDisk|SanDisk]] | archive-date = 2011-11-13 | archive-url = https://web.archive.org/web/20111113193538/http://sandisk.com/about-sandisk/press-room/press-releases/2010/2010-02-22-sandisk-ships-its-highest-capacity-sd-card-ever,-the-64gb-sandisk-ultra-sdxc-card | url-status = dead }}</ref>

In early 2011, Centon Electronics, Inc. (64&nbsp;GB and 128&nbsp;GB) and [[Company:Lexar|Lexar]] (128 GB) began shipping SDXC cards rated at Speed Class 10.<ref>{{cite web |last=Conneally |first=Tim |date=2011-03-16 |title=Lexar ships 128 GB Class 10 SDXC card; March 2011 |url=https://betanews.com/2011/03/16/lexar-ships-first-128gb-sdxc-cards |access-date=2024-01-22 |publisher=Betanews.com}}</ref> Pretec offered cards from 8&nbsp;GB to 128&nbsp;GB rated at Speed Class 16.<ref>{{cite web|url=http://www.pretec.com/news-event/press-room/item/root/sdxcsdhc-433x-c16 | title = SDXC/SDHC 433X Class 16 Card from Pretec|publisher=Pretec|date=2011-06-13|access-date= 2010-12-03}}</ref> In September 2011, SanDisk released a 64 GB microSDXC card.<ref>{{Citation | url = http://pocketnow.com/smartphone-news/first-64gb-microsd-card-arrives-when-will-smartphones-support | title = First 64GB microSD Card Here; When Will Smartphones Support It? | newspaper = Pocket now | date = 7 October 2017 | access-date = 4 October 2011 | archive-date = 11 October 2011 | archive-url = https://web.archive.org/web/20111011085002/http://pocketnow.com/smartphone-news/first-64gb-microsd-card-arrives-when-will-smartphones-support | url-status = dead }}</ref> Kingmax released a comparable product in 2011.<ref>{{Citation | url = https://www.engadget.com/2011/05/26/kingmax-flaunts-worlds-first-64gb-microsd-card/ | title = Kingmax flaunts world's first 64&nbsp;GB microSD card | newspaper = Engadget | date = 2011-05-26}}</ref>

In April 2012, Panasonic introduced MicroP2 card format for professional video applications. The cards are essentially full-size SDHC or SDXC UHS-II cards, rated at UHS Speed Class U1.<ref name="www2.panasonic.com">{{cite web |url=http://www2.panasonic.com/webapp/wcs/stores/servlet/prModelDetail?storeId=11301&catalogId=13251&itemId=696010&modelNo=Content03202013033731832&surfModel=Content03202013033731832 |title=For Journalists |publisher=.panasonic.com |date=2013-03-20 |access-date=2014-01-02 |url-status=dead |archive-url=https://web.archive.org/web/20130526104856/http://www2.panasonic.com/webapp/wcs/stores/servlet/prModelDetail?storeId=11301&catalogId=13251&itemId=696010&modelNo=Content03202013033731832&surfModel=Content03202013033731832 |archive-date=2013-05-26 }}</ref><ref>{{cite web|url=http://pro-av.panasonic.net/en/sales_o/p2/microP2/ |title=microP2 Card {{pipe}} P2 Series {{pipe}} Broadcast and Professional AV |publisher=Pro-av.panasonic.net |access-date=2014-01-02}}</ref> An adapter allows MicroP2 cards to work in current [[P2 (storage media)|P2 card]] equipment.<ref>{{cite web|last=Lawler |first=Richard |url=https://www.engadget.com/2012/04/15/panasonic-introduces-new-microp2-sd-sized-storage-at-nab-2012/ |title=Panasonic introduces new microP2 SD-sized storage at NAB 2012 |publisher=Engadget.com |date=2012-04-15 |access-date=2014-01-02}}</ref>

Panasonic MicroP2 cards shipped in March 2013 and were the first UHS-II compliant products on market; initial offer includes a 32 GB SDHC card and a 64 GB SDXC card.<ref name="www2.panasonic.com"/><ref>{{cite web|last=Renée |first=V |url=http://nofilmschool.com/2013/03/panasonic-microp2-card-april-release/ |title=Panasonic's New Smaller, Faster, and Lower-Cost MicroP2 Cards Coming in April, Starting at $250 « No Film School |date=23 March 2013 |publisher=Nofilmschool.com |access-date=2014-01-02}}</ref> Later that year, Lexar released the first 256&nbsp;GB SDXC card, based on 20&nbsp;nm NAND flash technology.<ref>{{cite web|title=Lexar Announces Industry's First 256&nbsp;GB SDXC UHS-I Memory Card|url=http://www.lexar.com/about/newsroom/press-releases/lexar-announces-industry-s-first-256gb-sdxc-uhs-i-memory-card|publisher=Micron | access-date =22 December 2012}}</ref>

In February 2014, SanDisk introduced the first 128&nbsp;GB microSDXC card,<ref>{{cite web|url=http://www.sandisk.com/about-sandisk/press-room/press-releases/2014/sandisk-introduces-worlds-highest-capacity-microsdxc-memory-card-at-128gb/|title=SANDISK INTRODUCES WORLD'S HIGHEST CAPACITY microSDXC MEMORY CARD AT 128GB|last=SanDisk|website=sandisk.com}}</ref> which was followed by a 200&nbsp;GB microSDXC card in March 2015.<ref>{{Cite web |url=http://www.sandisk.com/about-sandisk/press-room/press-releases/2015/200gb-sandisk-ultra-microsdxc-uhs-i-card-premium-edition/ |publisher=SanDisk.com
|title=SanDisk introduces the first 200GB microSDXC card |date=2014-02-24 |access-date=2016-06-06}}</ref> September 2014 saw SanDisk announce the first 512 GB SDXC card.<ref>{{Cite web|url=https://www.sandisk.com/about/media-center/press-releases/2014/sandisk-premieres-worlds-highest-capacity-sd-card-for-high-performance-video-and-photo-capture|title=SanDisk Premieres World's Highest Capacity SD Card for High Performance Video and Photo Capture|last=SanDisk|website=sandisk.com|access-date=2016-09-20}}</ref>

Samsung announced the world's first EVO Plus 256&nbsp;GB microSDXC card in May 2016,<ref>{{Cite web |url=https://news.samsung.com/global/samsung-electronics-introduces-the-evo-plus-256gb-microsd-card-with-the-highest-capacity-in-its-class |publisher=news.samsung.com |title=Samsung Electronics Introduces the EVO Plus 256 GB MicroSD Card, with the Highest Capacity in its Class |date=2016-05-10 |access-date=2016-06-06}}</ref> and in September 2016 [[Company:Western Digital|Western Digital]] (SanDisk) announced that a prototype of the first 1 TB{{efn|reference=except where stated otherwise, in this article 1 TB = 1000 billion bytes}} SDXC card would be demonstrated at Photokina.<ref>{{Cite web|url=https://www.sandisk.com/about/media-center/press-releases/2016/western-digital-demonstrates-prototype-of-the-worlds-first-1terabyte-SDXC-card|title=Western Digital Demonstrates Prototype of the World's First 1Terabyte SDXC Card|last=SanDisk|website=sandisk.com|access-date=2016-09-20}}</ref>

In August 2017, SanDisk launched a 400 GB microSDXC card.<ref>{{cite web|url=http://www.anandtech.com/show/11793/western-digital-launches-sandisk-ultra-microsd-card-with-400-gb-capacity|title=Western Digital Launches SanDisk Ultra microSD Card with 400 GB Capacity|first=Anton|last=Shilov}}</ref>

In January 2018, Integral Memory unveiled its 512 GB microSDXC card.<ref>{{Cite web|url=https://www.theverge.com/circuitbreaker/2018/1/22/16921108/integral-memory-512gb-microsd-card-largest-ever-memory-storage|title=Integral Memory's new 512GB microSD card is the biggest microSD card yet|last=Integral Memory|website=theverge.com|date=22 January 2018|access-date=2018-06-10}}</ref> In May 2018, [[Company:PNY Technologies|PNY]] launched a 512 GB microSDXC card. In June 2018 Kingston announced its Canvas series of MicroSD cards which were capable of capacities up to 512 GB,{{efn|name="GiB"|reference=here, 1 GB = 1 [[Byte#Units based on powers of 2|GiB]] = 2<sup>40</sup> B}}<!--GiB--> in three variations, Select, Go! and React.<ref>{{Cite web|url=https://www.kingston.com/en/company/press/article/50267?ArticleTitle=Kingston%20Digital%20Announces%20New%20%E2%80%98Canvas%E2%80%99%20Series%20of%20Flash%20Cards%20-%20(12%20March)|title=Kingston Digital Announces New 'Canvas' Series of Flash Cards |publisher=Kingston Technology Europe Co LLP|last=Kingston|access-date=2018-11-19}}</ref>

In February 2019, [[Company:Micron Technology|Micron]] and [[Company:SanDisk|SanDisk]] unveiled their microSDXC cards of 1 TB capacity.<ref>{{Cite web|url=https://www.theverge.com/2019/5/15/18626729/sandisks-1tb-microsd-card-available-b-h-photo-amazon-price|title=SanDisk's 1TB microSD card is now available|website=theverge.com|date=15 May 2019}}</ref>

=== 2019–present: SDUC ===
The Secure Digital Ultra Capacity (SDUC) format supports cards up to 128 TB{{efn|name="here, 1 TB = 1024"}} and offers speeds up to 985 MB/s.

== Capacity ==
Secure Digital includes five card families available in three sizes. The five families are the original Standard-Capacity (SDSC), the High-Capacity (SDHC), the eXtended-Capacity (SDXC), the Ultra-Capacity (SDUC) and the SDIO, which combines [[Input output|input/output]] functions with data storage.<ref name="sdcard_capacity">{{cite web|title=Capacity|publisher=SD Association |url=http://www.sdcard.org/developers/overview/capacity/|access-date=2011-12-08}}</ref><ref name="sdcard_using_sdxc">{{cite web|title=Using SDXC|publisher=SD Association|url=http://www.sdcard.org/consumers/sdxc_capabilities/using_sdxc/|access-date=2011-12-08|archive-date=2014-10-10|archive-url=https://web.archive.org/web/20141010090939/https://www.sdcard.org/consumers/sdxc_capabilities/using_sdxc|url-status=dead}}</ref><ref name="sdcard_sdio">{{cite web|title=SDIO|publisher=SD Association|url=http://www.sdcard.org/developers/overview/sdio/|access-date=2011-12-08}}</ref> The three form factors are the original size, the mini size and the micro size. Electrically passive adapters allow a smaller card to fit and function in a device built for a larger card. The SD card's small footprint is an ideal storage medium for smaller, thinner and more portable electronic devices.

=== <span class="anchor" id="SD"></span><span class="anchor" id="SDSC"></span> SD (SDSC) ===

[[File:SD-Logo.svg|thumb|upright=0.65|Secure Digital Standard Capacity (SD) logo. The specification defines cards with a capacity of up to {{Nowrap|2 GB}}.]]

The second-generation Secure Digital (SDSC or Secure Digital Standard Capacity) card was developed to improve on the MultiMediaCard (MMC) standard, which continued to evolve, but in a different direction. Secure Digital changed the MMC design in several ways:

* Asymmetrical shape of the sides of the SD card prevents inserting it upside down (whereas an MMC goes in most of the way but makes no contact if inverted).{{cn|date=September 2023}}
* Most standard size SD cards are {{Convert|2.1|mm|abbr=in}}<ref name=":0">{{Cite web |date=2020-12-11 |title=Capacity (SD/SDHC/SDXC/SDUC) {{!}} SD Association |url=https://www.sdcard.org/developers/sd-standard-overview/capacity-sd-sdhc-sdxc-sduc/ |access-date=2023-05-03 |website=sdcard.org |language=en-US}}</ref> thick, with microSD versions being {{Convert|1.0|mm|abbr=in}}<ref name=":0"/> thick, compared to {{Convert|1.4|mm|abbr=in}} for MMCs. The SD specification defines a card called '''Thin SD''' with a thickness of 1.4&nbsp;mm,{{fact|date=August 2023}} but they occur only rarely, as the SDA went on to define even smaller form factors.
* The card's electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user's fingers.
* The SD specification envisioned capacities and transfer rates exceeding those of MMC, and both of these functionalities have grown over time.{{cn|date=September 2023}} For a comparison table, see below.
* While MMC uses a single pin for data transfers, the SD card added a four-wire bus mode for higher data rates.{{cn|date=September 2023}}
* The SD card added Content Protection for Recordable Media (CPRM) security circuitry for [[Engineering:Digital rights management|digital rights management]] (DRM) content-protection.{{cn|date=September 2023}}
* Addition of a write-protect notch{{cn|date=September 2023}}

Full-size SD cards do not fit into the slimmer MMC slots, and other issues also affect the ability to use one format in a host device designed for the other.{{cn|date=September 2023}}

===SDHC===
[[File:SDHC-Logo.svg|thumb|upright=0.65|Secure Digital High Capacity (SDHC) logo. The specification defines cards with a capacity of more than {{No wrap|2 GB}} up to {{Nowrap|32 GB}}.]]

The Secure Digital High Capacity (SDHC) format, announced in January 2006 and defined in version 2.0 of the SD specification, supports cards with capacities up to 32&nbsp;GB.{{efn|name="GiB"}}<ref name="sdcard_capacity"/> The SDHC trademark is licensed to ensure compatibility.<ref name=sandisk-sdhc>[http://www.sandisk.com/Assets/File/pdf/retail/SDHC1.pdf What are SDHC, miniSDHC, and microSDHC?] SanDisk.  {{webarchive |url=https://web.archive.org/web/20080916035153/http://www.sandisk.com/Assets/File/pdf/retail/SDHC1.pdf |date=September 16, 2008 }}</ref>

SDHC cards are physically and electrically identical to standard-capacity SD cards (SDSC). The major compatibility issues between SDHC and SDSC cards are the redefinition of the Card-Specific Data (CSD) register in version 2.0 (see below), and the fact that SDHC cards are shipped preformatted with the [[FAT32]] file system.

Version 2.0 also introduces a high-speed bus mode for both SDSC and SDHC cards, which doubles the original Standard Speed clock to produce 25&nbsp;MB/s.<ref name=sd-association>[https://www.sdcard.org/developers/overview/bus_speed/ Bus Speed (Default Speed/ High Speed/ UHS)] SDcard.</ref>

SDHC host devices are required to accept older SD cards.<ref name="sdcard.org">[https://www.sdcard.org/consumers/compatibility/ About Compatibility with Host Devices] {{webarchive|url=https://web.archive.org/web/20111121065335/https://www.sdcard.org/consumers/compatibility/ |date=2011-11-21 }} SD Association.</ref> However, older host devices do not recognize SDHC or SDXC memory cards, although some devices can do so through a firmware upgrade.<ref>[http://www.jetaudio.com/download/cowon_rn_d2.html#241 What's new in Firmware 2.41 Beta (for COWON D2)] JetAudio.</ref>{{Better source needed|date=June 2021}} Older Windows operating systems released before Windows 7 require patches or service packs to support access to SDHC cards.<ref>{{cite web|url= http://support.microsoft.com/kb/934428 | work= Support | title = 934428 – Hotfix for Windows XP that adds support for SDHC cards that have a capacity of more than 4&nbsp;GB |publisher= Microsoft |date=2008-02-15 |access-date=2010-08-22}}</ref><ref>{{cite web|url=http://support.microsoft.com/kb/939772 | work = Support | title = 939772 – Some Secure Digital (SD) cards may not be recognized in Windows Vista |publisher= Microsoft |date= 2008-05-15 |access-date= 2010-08-22}}</ref><ref>{{cite web |url= http://support.microsoft.com/kb/949126 | work = Support | title = 949126 – A Secure Digital High Capacity (SDHC) card is not recognized on a Windows Vista Service Pack 1-based computer |publisher= Microsoft |date= 2008-02-21 |access-date= 2010-08-22}}</ref>

===SDXC===
[[File:SDXC.svg|thumb|upright=0.65|Secure Digital eXtended Capacity logo. The specification defines cards with a capacity of more than {{No wrap|32 GB}} up to {{Nowrap|2 TB}}.]]

The Secure Digital eXtended Capacity (SDXC) format, announced in January 2009 and defined in version 3.01 of the SD specification, supports cards up to 2&nbsp;TB,{{efn|name="here, 1 TB = 1024"}} compared to a limit of 32&nbsp;GB{{efn|name="GiB"}} for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's [[ExFAT|exFAT]] file system as a mandatory feature.<ref>{{Cite web |url=https://www.sdcard.org/developers/overview/capacity/ |title=Capacity (SD/SDHC/SDXC) |website=SD Association |language=en |access-date=2017-03-20}}</ref>

Version 3.01 also introduced the Ultra High Speed (UHS) bus for both SDHC and SDXC cards, with interface speeds from 50&nbsp;MB/s to 104&nbsp;MB/s for four-bit UHS-I bus.<ref name="BS">{{cite web |title=Bus Speed (Default Speed/ High Speed/ UHS) |url=https://www.sdcard.org/developers/overview/bus_speed/ |website=SD Association |access-date=20 March 2017 |language=en}}</ref> (this number has since been exceeded with SanDisk proprietary technology for 170&nbsp;MB/s read, which is not proprietary anymore, as Lexar has the 1066x running at 160&nbsp;MB/s read and 120&nbsp;MB/s write via UHS&nbsp;1, and Kingston also has their Canvas Go! Plus, also running at 170&nbsp;MB/s).<ref>{{Cite web |title=Lexar Professional 1066x microSDXC UHS-I Card SILVER Series |url=https://www.lexar.com/portfolio_page/professional-1066x-microsdhcmicrosdxc-uhs-i-cards-silver-series/ |access-date=2021-04-10 |website=Lexar |language=en |archive-url=https://web.archive.org/web/20210410090638/https://www.lexar.com/portfolio_page/professional-1066x-microsdhcmicrosdxc-uhs-i-cards-silver-series/ |archive-date=2021-04-10}}</ref><ref>{{Cite web |title=SanDisk Extreme PRO SDHC And SDXC UHS-I Card |url=https://shop.westerndigital.com/products/memory-cards/sandisk-extreme-pro-uhs-i-sd#SDSDXXY-064G-GN4IN |access-date=2021-04-10 |website=shop.westerndigital.com}}</ref><ref>{{Cite web |title=Canvas Go! Plus Class 10 SD Cards – UHS-I, U3, V30 – 64&nbsp;GB–512&nbsp;GB |url=https://www.kingston.com/en/memory-cards/canvas-go-plus-sd-card |access-date=2021-04-10 |website=Kingston Technology Company |language=en-US}}</ref><ref>{{Cite web |title=Canvas Go! Plus Class 10 microSD Cards – V30, A2 – 64&nbsp;GB–512&nbsp;GB |url=https://www.kingston.com/en/memory-cards/canvas-go-plus-microsd-card |access-date=2021-04-10 |website=Kingston Technology Company |language=en-US}}</ref>

Version 4.0, introduced in June 2011, allows speeds of 156&nbsp;MB/s to 312&nbsp;MB/s over the four-lane (two differential lanes) UHS-II bus, which requires an additional row of physical pins.<ref name="BS"/>

Version 5.0 was announced in February 2016 at CP+ 2016, and added "Video Speed Class" ratings for UHS cards to handle higher resolution video formats like [[8K resolution|8K]].<ref name="sda_video_speed">{{cite web | url = https://www.sdcard.org/press/New_SD_Association_Speed_Class_Supports_8K_and_Multi_File_Video_Recording.pdf | date = 2016-02-26 | title = NEW SD ASSOCIATION VIDEO SPEED CLASS SUPPORTS 8K AND MULTI-FILE VIDEO RECORDING | publisher = SD Association | access-date = 2016-03-03 | archive-date = 2016-03-07 | archive-url = https://web.archive.org/web/20160307192442/https://www.sdcard.org/press/New_SD_Association_Speed_Class_Supports_8K_and_Multi_File_Video_Recording.pdf | url-status = dead }}</ref><ref>{{cite web | url = http://www.anandtech.com/show/10105/sd-association-announces-50-specification | title = SD Association Announces SD 5.0 Specification: SD Cards For UHD and 360° Video Capture | date = 2016-03-01 | first = Anton | last = Shilov | publisher = Anand Tech }}</ref> The new ratings define a minimal write speed of 90&nbsp;MB/s.<ref name="sd50_video_speed">{{cite web | url = https://www.sdcard.org/downloads/pls/latest_whitepapers/Video_Speed_Class-The_new_capture_protocol_of_SD_5.0.pdf | title = Video Speed Class: The new capture protocol of SD 5.0 | publisher = SD Association | date = February 2016 | access-date = 2016-03-03 | archive-date = 2016-12-23 | archive-url = https://web.archive.org/web/20161223213758/https://www.sdcard.org/downloads/pls/latest_whitepapers/Video_Speed_Class-The_new_capture_protocol_of_SD_5.0.pdf | url-status = dead }}</ref><ref>{{cite web | url = https://www.cinema5d.com/new-video-speed-class-for-sd-cards/ | title = New Video Speed Class for SD Cards | first = Fabian | last =  Chaundy | date = 2016-02-26 | work = cinema5D }}</ref>

===SDUC===
[[File:SDUC.svg|thumb|upright=0.65|Secure Digital Ultra Capacity (SDUC) logo. The specification defines cards with a capacity of more than {{No wrap|2 TB}} up to {{Nowrap|128 TB}}.]]

The Secure Digital Ultra Capacity (SDUC) format, described in the SD 7.0 specification, and announced in June 2018, supports cards up to 128 TB{{efn|name="here, 1 TB = 1024"}} and offers speeds up to 985 MB/s, regardless of form factor, either micro or full size, or interface type including UHS-I, UHS-II, UHS-III or SD Express.<ref>{{cite web |title=SD Express Cards with PCIe and NVMeTM Interfaces |url=https://www.sdcard.org/downloads/pls/latest_whitepapers/SD_Express_Cards_with_PCIe_and_NVMe_Interfaces_White_Paper.pdf |publisher=SD Association |access-date=21 November 2018 |date=June 2018 |archive-url=https://web.archive.org/web/20201112011753/https://www.sdcard.org/downloads/pls/latest_whitepapers/SD_Express_Cards_with_PCIe_and_NVMe_Interfaces_White_Paper.pdf |archive-date=2020-11-12}}</ref> The SD Express interface can also be used with SDHC and SDXC cards.

====exFAT filesystem====
{{Main|ExFAT}}

SDXC and SDUC cards are normally formatted using the [[ExFAT|exFAT]] file system, thereby limiting their use to a limited set of operating systems.<ref name=":0"/>

[[Software:Windows Vista|Windows Vista]] (SP1) and later<ref>{{cite web |title=Notable Changes in Windows Vista Service Pack 1 |url=https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-vista/cc709618(v=ws.10) |department=TechNet |website=[[Software:Microsoft Docs|Microsoft Docs]] | date=25 July 2008 |access-date=2021-11-07}}</ref> and [[Software:OS X|OS X]] (10.6.5 and later) have native support for exFAT.<ref>{{cite web|url=http://support.apple.com/kb/HT3553 |title=About the SD and SDXC card slots |publisher=Apple Inc. |date=2011-05-03 |access-date=2011-09-05}}</ref><ref>{{cite web |url=http://www.tuxera.com/mac/apple-released-exfat-support-in-os-x-10-6-5-update/ |title=Apple released exFAT support in OS X 10.6.5 update |publisher=Tuxera.com |date=2010-11-22 |access-date=2012-01-04 |archive-date=2012-05-13 |archive-url=https://web.archive.org/web/20120513202527/http://www.tuxera.com/mac/apple-released-exfat-support-in-os-x-10-6-5-update/ |url-status=dead }}</ref> (Windows XP and Server 2003 can support exFAT via an optional update from Microsoft.)<ref>{{cite web|author=WindowsXP-KB955704-x86-ENU.exe |url=https://support.microsoft.com/en-us/kb/955704|title=Description of the exFAT file system driver update package|publisher=Microsoft.com|date=2011-10-08|access-date=2015-11-27}}</ref>

Most [[Software:Berkeley Software Distribution|BSD]] and [[Software:Linux|Linux]] distributions did not for legal reasons, though in Linux kernel 5.4 Microsoft open-sourced the spec and allowed the inclusion of an exFAT driver.<ref>{{cite web|url=https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.4-exFAT-Is-Coming |title=The Initial exFAT Driver Queued For Introduction With The Linux 5.4 Kernel |publisher=phoronix.com |date=2019-08-30 |access-date=2020-02-05}}</ref> Users of older kernels or BSD can manually install third-party implementations of exFAT (as a [[Software:Filesystem in Userspace|FUSE]] module) in order to be able to mount exFAT-formatted volumes.<ref>{{cite web|url=https://code.google.com/p/exfat/ |title=exFAT for BSD and Linux systems from Google Code |access-date=2014-01-02}}</ref> However, SDXC cards can be reformatted to use any file system (such as [[Ext4|ext4]], [[Unix File System|UFS]], [[VFAT]] or [[NTFS]]), alleviating the restrictions associated with exFAT availability.

Except for the change of file system, SDXC cards are mostly backward compatible with SDHC readers, and many SDHC host devices can use SDXC cards if they are first reformatted to the FAT32 file system.<ref>{{cite web |title=Updated: How to upgrade your 3DS SD card, to 64GB and beyond |author=deKay |date=15 January 2015 |website=Lofi-Gaming |url=https://lofi-gaming.org.uk/blog/2013/10/25/updated-how-to-upgrade-your-3ds-sd-card-to-64gb-and-beyond/ |access-date=2018-12-21}}</ref><ref>{{cite web |title=Ask Hackaday: How On Earth Can A 2004 MP3 Player Read An SDXC Card? |first=Jenny |last=List |date=29 November 2017 |website=Hackaday |url=https://hackaday.com/2017/11/29/ask-hackaday-how-on-earth-can-a-2004-mp3-player-read-an-sdxc-card/ |access-date=2018-12-21}}</ref><ref>{{cite web |title=High capacity microSD cards and Android – Gary explains |first=Gary |last=Sims |date=9 May 2016 |website=Android Authority |url=https://www.androidauthority.com/high-capacity-microsd-cards-android-gary-explains-690710/ |access-date=2018-12-21}}</ref>

The SD Association provides a formatting utility for Windows and Mac OS X that checks and formats SD, SDHC, SDXC and SDUC cards.<ref>{{cite web|url=https://www.sdcard.org/downloads/formatter_4/ |title=SD Formatter 4.0 for SD/SDHC/SDXC – SD Association |publisher=Sdcard.org |access-date=2014-01-02}}</ref>

=== Comparison ===
{| class="wikitable" style="text-align: center;"
|+ Comparison of SD card capacity standards<ref>{{Cite web|url=https://www.sdcard.org/developers/overview/capacity/index.html|title=Capacity (SD/SDHC/SDXC/SDUC) – SD Association|website=sdcard.org|access-date=2019-02-15}}</ref>
! colspan="2" |
! scope="col" | SD
! scope="col" | SDHC
! scope="col" | SDXC
! scope="col" | SDUC
|- style="background: white;"
! colspan="2" |Logo
| [[File:SD-Logo.svg|frameless|upright=0.4]]
| [[File:SDHC-Logo.svg|frameless|upright=0.4]]
| [[File:SDXC-Logo.svg|frameless|upright=0.4]]
| [[File:SDUC.svg|frameless|upright=0.4]]
|-
! rowspan="2" |Capacity
!Min
|0
|>2 GB
|>32 GB
|>2 TB
|-
!Max
|2 GB
|32 GB
|2 TB
|128 TB
|-
! colspan="2" |Typical FS
|[[FAT12]]/[[FAT16]]
|[[FAT32]]
| colspan="2" |[[ExFAT|exFAT]]
|}

== Speed ==
SD card speed is customarily rated by its sequential read or write speed. The sequential performance aspect is the most relevant for storing and retrieving large files (relative to block sizes internal to the [[Flash memory|flash memory]]), such as images and multimedia. Small data (such as file names, sizes and timestamps) falls under the much lower [[IOPS|speed limit of random access]], which can be the limiting factor in some use cases.<ref name="necstudy">{{Citation | url = http://static.usenix.org/events/fast/tech/full_papers/Kim.pdf | title = Revisiting Storage for Smartphones | first1 = H | last1 = Kim | first2 = N | last2 = Agrawal | first3 = C | last3 = Ungureanu | publisher = NEC Laboratories | place = America | at = table 3|date=2012-01-30|quote=Speed class considered irrelevant: our benchmarking reveals that the "speed class" marking on SD cards is not necessarily indicative of application performance; although the class rating is meant for sequential performance, we find several cases in which higher-grade SD cards performed worse than lower-grade ones overall.}}</ref><ref name= "Gough2014">{{cite web|last=Lui|first=Gough|title=SD Card Sequential, Medium & Small Block Performance Round-Up|url= http://goughlui.com/2014/01/16/testing-sd-card-performance-round-up/ |website=Gough's techzone|access-date=29 November 2015|date=2014-01-16|quote=Variations in 4k small block performance saw a difference of approximately 300-fold between the fastest and slowest cards. Distressingly, many of the tested cards were mediocre to poor on that metric, which may explain why running updates on Linux running off SD cards can take a very long time.}}</ref><ref>{{cite web|url= http://www.raspberrypi.org/forums/viewtopic.php?t=4076|title=Raspberry Pi forum: SD card benchmarks|access-date=2014-08-12}}</ref>

With early SD cards, a few card manufacturers specified the speed as a "times" ("×") rating, which compared the average speed of reading data to that of the original [[CD-ROM]] drive. This was superseded by the '''Speed Class Rating''', which guarantees a minimum rate at which data can be written to the card.<ref name="sda_speed_class">{{cite web |title= SD Speed Class | url= https://www.sdcard.org/developers/overview/speed_class |url-status=dead |archive-url=https://web.archive.org/web/20201221172542/https://www.sdcard.org/developers/overview/speed_class/ |archive-date=2020-12-21 |access-date=2013-11-13 |publisher=SDCard.org}}</ref>

The newer families of SD card improve card speed by increasing the bus rate (the frequency of the clock signal that strobes information into and out of the card). Whatever the bus rate, the card can signal to the host that it is "busy" until a read or a write operation is complete. Compliance with a higher speed rating is a guarantee that the card limits its use of the "busy" indication.

=== Bus===

==== Default Speed ====
SD Cards will read and write at speeds of 12.5 MB/s.

==== High Speed ====
High-Speed Mode (25 MB/s) was introduced to support digital cameras with 1.10 spec version.<ref>{{Cite web|url= https://www.sdcard.org/developers/overview/bus_speed/ |title=Bus Speed (Default Speed/High Speed/UHS/SD Express) | publisher = SD Association|website= SD card |access-date=2020-04-18}}</ref>

====<span class="anchor" id="Ultra High Speed"></span><span class="anchor" id="UHS"></span> Ultra High Speed (UHS) ====
The Ultra High Speed (UHS) bus is available on some SDHC and SDXC cards.<ref name="sda_bus_speed">{{cite web|url= https://www.sdcard.org/developers/overview/bus_speed/ |title=Bus Speed (Default Speed/ High Speed/ UHS) | publisher = SD Association | work =SD card |access-date=2013-11-13}}</ref><ref>{{cite web| url= https://www.engadget.com/2010/06/24/sd-cards-branded-with-an-upper-case-i-are-faster-yo/ |title=SD cards branded with an upper-case 'I' are faster, yo |publisher=Engadget|date= 2010-06-24 |access-date=2010-08-22}}</ref><ref>{{cite web |last=Rigg |first=Jamie |url= https://www.engadget.com/2013/07/16/toshiba-exceria-pro-sd-cards/ |title= Toshiba's Exceria Pro SDHC cards claim 'world's fastest' write speeds of 240&nbsp;MB per second | work=Engadget |date=2013-07-16 |access-date= 2014-01-02}}</ref> 

Cards that comply with UHS show Roman numerals 'I', 'II' or 'III' next to the SD card logo,<ref name="sda_bus_speed"/><ref name= "sda_speed_class"/> and report this capability to the host device. Use of UHS-I requires that the host device command the card to drop from 3.3-volt to 1.8-volt operation over the I/O interface pins and select the four-bit transfer mode, while UHS-II requires 0.4-volt operation.

The higher speed rates of UHS-II and III are achieved by using two-lane 0.4&nbsp;V [[Engineering:Low-voltage differential signaling|low-voltage differential signaling]] (LVDS) on a second row of pins.<ref>{{cite web |title=SD Standard Overview |url=https://www.sdcard.org/developers/sd-standard-overview/ |website=SD Association |access-date=19 June 2023}}</ref> Each lane is capable of transferring up to 156&nbsp;MB/s. In full-duplex mode, one lane is used for Transmit while the other is used for Receive. In half-duplex mode both lanes are used for the same direction of data transfer allowing a double data rate at the same clock speed. In addition to enabling higher data rates, the UHS-II interface allows for lower interface power consumption, lower I/O voltage and lower electromagnetic interference (EMI).

The following ultra-high speeds are specified:

===== UHS-I =====
Specified in SD version 3.01.<ref name="SDHCspec">{{cite web | publisher = SD Association | url = http://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf | title = SD Part 1, Physical Layer Simplified Specification, Version 3.01 | date = 2010-05-18 | access-date = 2013-11-25 | archive-url = https://web.archive.org/web/20131205014133/https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf | archive-date = 2013-12-05 | url-status = dead }}</ref> <!-- There is a newer 2017 version at https://www.sdcard.org/downloads/pls/ but it has a complicated little onScroll JS to ensure you've "read" ("yeah, right..") the license terms, which doesn't seem to work. --> Supports a clock frequency of 100&nbsp;MHz (a quadrupling of the original "Default Speed"), which in four-bit transfer mode could transfer 50&nbsp;MB/s (SDR50). UHS-I cards declared as '''UHS104''' (SDR104) also support a clock frequency of 208&nbsp;MHz, which could transfer 104&nbsp;MB/s. [[Engineering:Double data rate|Double data rate]] operation at 50&nbsp;MHz (DDR50) is also specified in Version 3.01, and is mandatory for microSDHC and microSDXC cards labeled as UHS-I. In this mode, four bits are transferred when the clock signal rises and another four bits when it falls, transferring an entire byte on each full clock cycle, hence a 50&nbsp;MB/s operation could be transferred using a 50&nbsp;MHz clock.

There is a proprietary UHS-I extension, called DDR200, originally created by SanDisk that increases transfer speed further to 170&nbsp;MB/s. Unlike UHS-II, it does not use additional pins. It achieves this by using the 208&nbsp;MHz frequency of the standard SDR104 mode, but using DDR transfers.<ref>{{Cite web |title=SanDisk Extreme microSDXC datasheet |url=https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/sandisk/product/memory-cards/extreme-uhs-i-microsd/data-sheet-extreme-uhs-i-microsd.pdf |website=Western Digital}}</ref><ref>{{Cite web |website=Genesys Logic |title=GL3232 |url=http://www.genesyslogic.com/en/product_view.php?show=83}}</ref> This extension has since then been used by Lexar for their 1066x series (160&nbsp;MB/s), Kingston Canvas Go Plus (170&nbsp;MB/s) and the MyMemory PRO SD card (180&nbsp;MB/s).

===== UHS-II =====
[[File:Lexar 1000x MicroSDHC UHS-II U3 Class 10 - Back.jpg|thumb|upright|Back side of a Lexar UHS-II microSDHC card, showing the additional row of UHS-II connections]]

Specified in version 4.0, further raises the data transfer rate to a theoretical maximum of 156&nbsp;MB/s (full-[[Engineering:Duplex (telecommunications)|duplex]]) or 312&nbsp;MB/s (half-duplex) using an additional row of pins for LVDS signalling<ref name="firstsdxc">{{cite web | url = https://www.sdcard.org/press/SD_Association_Announces_UHS-II_eBOOK_Jan_5_2011_ENGLISH.PDF | publisher = SD Card | title = Association Triples Speeds with UHS-II | date = 5 January 2011 | access-date = 2011-08-09 | archive-date = 2011-03-21 | archive-url = https://web.archive.org/web/20110321195143/http://www.sdcard.org/press/SD_Association_Announces_UHS-II_eBOOK_Jan_5_2011_ENGLISH.PDF | url-status = dead }}</ref> (a total of 17 pins for full-size and 16 pins for micro-size cards).<ref name="sda_bus_speed"/> While first implementations in compact system cameras were seen three years after specification (2014), it took many more years until UHS-II was implemented on a regular basis. At the beginning of 2024, almost 90 DSLR and mirrorless cameras support UHS-II.<ref>{{cite web |url=https://www.memorycard-lab.com/-Article/UHS-II-Cameras | publisher = memorycard-lab.com | title = UHS-II camera list | access-date=2024-01-19}}</ref>

===== UHS-III =====
Version 6.0, released in February 2017, added two new data rates to the standard. FD312 provides 312 MB/s while FD624 doubles that. Both are full-duplex. The physical interface and pin-layout are the same as with UHS-II, retaining backward compatibility.<ref>{{Cite web|url=https://www.sdcard.org/press/DoublesTransferSpeeds_with_UHS3_2_9_2017.pdf|title=SD Association Doubles Bus Interface Speeds with UHS-III|date=23 February 2017|access-date=23 February 2017|archive-date=24 February 2017|archive-url=https://web.archive.org/web/20170224211349/https://www.sdcard.org/press/DoublesTransferSpeeds_with_UHS3_2_9_2017.pdf|url-status=dead}}</ref>

==== <span class="anchor" id="Express"></span> SD Express ====
[[File:SD Express Highest Speed Card Standard.jpg|thumb|Front and back of an SD Express card]]

The SD Express bus was released in June 2018 with SD specification 7.0. It uses a single PCIe lane to provide full-duplex 985 MB/s transfer speed. Supporting cards must also implement the [[Engineering:NVM Express|NVM Express]] storage access protocol. The Express bus can be implemented by SDHC, SDXC and SDUC cards. For legacy application use, SD Express cards must also support High-Speed bus and UHS-I bus. The Express bus re-uses the pin layout of UHS-II cards and reserves the space for additional two pins that may be introduced in the future.<ref>{{cite web | work = Card wave services | date = July 2018 |url= http://www.cardwaveservices.com/2018/07/change-for-the-better-introducing-sd-express/ |title=Introducing SD Express|access-date=23 December 2018}}</ref>

Hosts which implement version 7.0 of the spec allow SD Cards to do [[Direct memory access|direct memory access]], which increases the attack surface of the host dramatically in the face of malicious SD cards.<ref>{{Cite web|url= https://www.ndss-symposium.org/ndss-paper/thunderclap-exploring-vulnerabilities-in-operating-system-iommu-protection-via-dma-from-untrustworthy-peripherals/|title=Thunderclap: Exploring Vulnerabilities in Operating System IOMMU Protection via DMA from Untrustworthy Peripherals |publisher=NDSS Symposium |language=en-US |access-date=2019-08-06}}</ref>

Version 8.0 was announced on 19 May 2020, with support for two PCIe lanes with an additional row of contacts and PCIe 4.0 transfer rates, for a maximum bandwidth of 3938 MB/s.<ref>{{Cite press release|title= SDExpress Delivers New Gigabtye Speeds For SDMemory Cards | work = SD card | publisher = SD association |url= https://www.sdcard.org/press/whatsnew/SDExpressDeliversNewGigabtyeSpeedsForSDMemoryCards.pdf}}</ref>

Version 9.0 was released in February 2022.<ref>{{Cite web |title=sd 9.0 |url=https://www.sdcard.org/cms/wp-content/uploads/2022/05/SD-SPECIFICATION-9-%E2%80%93NEW-OPPORTUNITIES-FOR-SD-MEMORY-CARDS_EN.pdf}}</ref>

===== <span class="anchor" id="microExpress"></span> microSD Express =====
In February 2019, the SD Association announced microSD Express.<ref>{{cite news |last=Gartenberg |first=Chain |title=Memory cards are about to get much faster with new microSD Express spec |url= https://www.theverge.com/circuitbreaker/2019/2/25/18239558/microsd-express-sd-association-new-format-speed-faster-mwc-2019-data-transfer |access-date=18 March 2019 |work=The Verge |date=25 February 2019}}</ref> The microSD Express cards offer PCI Express and NVMe interfaces, as the June 2018 SD Express release did, alongside the legacy microSD interface for continued backwards compatibility. The SDA also released visual marks to denote microSD Express memory cards to make matching the card and device easier for optimal device performance.<ref>{{cite news |last=Henchman |first=Mark |title=The microSD Express standard combines PCI Express speeds, microSD convenience |url=https://www.pcworld.com/article/3343067/the-microsd-express-standard-combines-pci-express-speeds-microsd-convenience.html |access-date=18 March 2019 |date=25 February 2019}}</ref>

==== Bus speed comparison ====
{| class="wikitable" style="text-align: center;"
|+ Comparison of SD card bus speeds<ref>{{Cite web|url= https://www.sdcard.org/developers/overview/bus_speed/ |title=Bus Speed (Default Speed/High Speed/UHS/SD Express) | publisher = SD Association|website= SD card |access-date=2019-02-15}}</ref>
! Scope="col" rowspan="2" | Bus interface
! Scope="col" rowspan="2" | Bus logo
! Scope="col" rowspan="2" | Bus speed
! rowspan="2" | [[Engineering:PCI Express|PCI Express]] lanes
! rowspan="2" | [[Engineering:Duplex (telecommunications)|Duplex]]
! Scope="col" colspan="4" | Card types
! Scope="col" rowspan="2" | Spec version
|-
! Scope="col" | SD
! Scope="col" | SDHC
! Scope="col" | SDXC
! Scope="col" | SDUC
|-
! Scope="row" | {{Nowrap|Default Speed}}
| rowspan="2" {{N/a}}
| {{Nowrap|{{0|00,0}}12.5 MB/s}}
| rowspan="9" {{N/a}}
| rowspan="2" {{dunno}}
| rowspan="2" {{Yes}}
| rowspan="13" {{Yes}}
| rowspan="13" {{Yes}}
| rowspan="13" {{Yes}}
| 1.01
|-
! Scope="row" | {{Nowrap|High Speed}}
| {{Nowrap|{{0|00}}25 MB/s}}
| 1.10
|-
! rowspan="3" scope="row" | UHS-I
| rowspan="2" style="text-align: center;" | [[File:UHS-I.svg|x20px]]
| {{Nowrap|{{0|00}}50 MB/s}}
| {{Nowrap|Half / Full}}
| rowspan="11" {{No}}
| rowspan="2" | 3.01
|-
| {{Nowrap|{{0|0}}104 MB/s}}
| rowspan="2" | Half
|-
| {{N/a}}
| {{Nowrap|{{0|0}}180 MB/s}}{{Efn|This speed is achievable using DDR208 controller.}}
| {{N/a}}
|-
! rowspan="2" scope="row" | UHS-II
| Rowspan="2" style="text-align: center;" | [[File:UHS-II.svg|x20px]]
| {{Nowrap|{{0|0}}156 MB/s}}
| Full
| rowspan="2" | 4.00
|-
| {{Nowrap|{{0|0}}312 MB/s}}
| Half
|-
! rowspan="2" scope="row" | UHS-III
| rowspan="2" style="text-align: center;" | [[File:UHS-III.svg|x20px]]
| {{Nowrap|{{0|0}}312 MB/s}}
| rowspan="6" | Full
| rowspan="2" | 6.0{{0|0}}
|-
| {{Nowrap|{{0|0}}624 MB/s}}
|-
! rowspan="4" scope="row" | SD Express
| rowspan="4" style="text-align: center;" | [[File:SDex(short).svg|x20px]] <br/> [[File:SDexpress.svg|x20px]]
| {{Nowrap|{{0|0}}985 MB/s}}
| 3.1 ×1 
| 7.0{{0|0}}
|-
| rowspan="2"| {{Nowrap|1969 MB/s}} 
| 3.1 ×2
| rowspan="3"| 8.0{{0|0}}
|-
| 4.0 ×1  
|-
| {{Nowrap|3938 MB/s}} 
| 4.0 ×2 
|}

==== Compatibility ====
{| class="wikitable" style="text-align: center;"
|+Bus speed of host and card combinations (in MB/s)<ref>{{Cite journal|date=June 2018|title=SD Express Cards with Pie and Name Interfaces|url=https://www.sdcard.org/downloads/pls/latest_whitepapers/SD_Express_Cards_with_PCIe_and_NVMe_Interfaces_White_Paper.pdf|journal=SD Association|pages=9|access-date=2018-06-27|archive-date=2020-11-12|archive-url=https://web.archive.org/web/20201112011753/https://www.sdcard.org/downloads/pls/latest_whitepapers/SD_Express_Cards_with_PCIe_and_NVMe_Interfaces_White_Paper.pdf|url-status=dead}}</ref>
! colspan="2" rowspan="2" {{Diagonal split header 2|Card|Host}}
! colspan="2" | UHS-I
! colspan="2" | UHS-II
! rowspan="2" | UHS-III
! rowspan="2" | Express
|-
! UHS50
! UHS104
! {{Abbr|Full|Full-duplex}}
! {{Abbr|Half|Half-duplex}}
|-
! rowspan="2" |UHS-I
! UHS50
|'''{{0|0}}50'''
|{{0|0}}50
|{{0|0}}50
|{{0|0}}50
|{{0|0}}50
|{{0|0}}50
|-
! UHS104
|{{0|0}}50
|'''104'''
|104
|104
|104
|104
|-
! rowspan="2" |UHS-II
! {{Abbr|Full|Full-duplex}}
|{{0|0}}50
|104
|'''156'''
|156
|156
|104
|-
! {{Abbr|Half|Half-duplex}}
|{{0|0}}50
|104
|156
|'''312'''
|312
|104
|-
! colspan="2" |UHS-III
|{{0|0}}50
|104
|156
|312
|'''624'''
|104
|-
! colspan="2" |Express
|{{0|0}}50
|104
|104
|104
|104
|'''985'''
|}
NOTE: If the card reader uses the DDR208 controller on the UHS 1 pins, the card reader will perform at 180 MB/s on applicable UHS 1 cards

=== Class ===
[[File:Sandisk microSDXC 64GB Ultra.jpg|thumb|64 GB SanDisk Ultra microSDXC card (with UHS-I and UHS Speed Class 1 markings)]]
[[File:Lexar 1000x MicroSDHC UHS-II U3 Class 10 - Front.jpg|thumb|32 GB Lexar 1000x microSDHC card (with UHS-II and UHS Speed Class 3 markings)]]

[[File:Sony Tough SF-M64T SDUHSIIBEIDE.png|thumb|The front and back of the Sony 64GB SF-M Tough Series UHS-II SDXC Memory Card]]

The [[Organization:SD Association|SD Association]] defines standard speed classes for SDHC/SDXC cards indicating minimum performance (minimum serial data writing speed). Both read and write speeds must exceed the specified value. The specification defines these classes in terms of performance curves that translate into the following minimum read-write performance levels on an empty card and suitability for different applications:<ref name="SDHCspec"/><ref name="sda_speed_class"/><ref name="sda_speed_class_consumer">{{cite web|url=https://www.sdcard.org/consumers/choices/speed_class/index.html|title=Speed Class Standards for Video Recording – SD Association|website=sdcard.org}}</ref><ref name="sda_logos_2017">{{Cite web|url=https://www.sdcard.org/consumers/pdf/2017SDA_brochure_eng.pdf|title=SD Standards Brochure 2017|access-date=2017-03-29|archive-date=2017-03-30|archive-url=https://web.archive.org/web/20170330174639/https://www.sdcard.org/consumers/pdf/2017SDA_brochure_eng.pdf|url-status=dead}}</ref>

The SD Association defines three types of Speed Class ratings: the original Speed Class, UHS Speed Class and Video Speed Class.

==== (Original) Speed Class ====
'''Speed Class''' ratings 2, 4 and 6 assert that the card supports the respective number of megabytes per second as a minimum sustained write speed for a card in a fragmented state.

Class 10 asserts that the card supports 10&nbsp;MB/s as a minimum non-fragmented sequential write speed and uses a High Speed bus mode.<ref name="SDHCspec"/> The host device can read a card's speed class and warn the user if the card reports a speed class that falls below an application's minimum need.<ref name="SDHCspec"/> By comparison, the older "×" rating measured maximum speed under ideal conditions, and was vague as to whether this was read speed or write speed.

The graphical symbol for the speed class has a number encircled with 'C' (C2, C4, C6 and C10).

==== UHS Speed Class ====
UHS-I and UHS-II cards can use '''UHS Speed Class''' rating with two possible grades: class 1 for minimum write performance of at least 10&nbsp;MB/s ('U1' symbol featuring number 1 inside 'U') and class 3 for minimum write performance of 30&nbsp;MB/s ('U3' symbol featuring 3 inside 'U'), targeted at recording 4K video.<ref>{{cite web|url=https://www.sdcard.org/home/New_SDXC_and_SDHC_Memory_Cards_Now_Support_4K2K_Video_11-6-2013_FINAL_2.pdf |title=NEW SDXC AND SDHC MEMORY CARDS SUPPORT 4K2K VIDEO |publisher=SD Association |access-date=2013-11-13}}</ref> Before November 2013, the rating was branded ''UHS Speed Grade'' and contained grades 0 (no symbol) and 1 ('U1' symbol). Manufacturers can also display standard speed class symbols (C2, C4, C6 and C10) alongside, or in place of UHS speed class.

UHS memory cards work best with UHS host devices. The combination lets the user record HD resolution videos with tapeless camcorders while performing other functions. It is also suitable for real-time broadcasts and capturing large HD videos.

==== Video Speed Class ====
'''Video Speed Class''' defines a set of requirements for UHS cards to match the modern [[Multi-level cell|MLC NAND flash]] memory<ref name="sd50_video_speed"/> and supports progressive 4K and 8K video with minimum sequential writing speeds of 6 – 90&nbsp;MB/s.<ref name="sda_video_speed"/><ref name="sda_speed_class"/><ref name="sda_speed_class_consumer"/> The graphical symbols use a stylized 'V' followed by a number designating write speed (''i.e.'' V6, V10, V30, V60 and V90).

==== Comparison ====
{{Multiple image
| direction      = vertical
| image1         = Panasonic CFEXPRESS CARD 128 GB & SAMSUNG SD CARD PRO PLUS 256 GB (2021 EDITION) FRONT.jpg
| image2         = Panasonic CFEXPRESS CARD 128 GB & SAMSUNG SD CARD PRO PLUS 256 GB (2021 EDITION) REAR.jpg
| footer         = '''Top:''' A 128 GB [[CFexpress]] Type B card by [[Company:Panasonic|Panasonic]] (1700 MBit/s reading) next to 256 GB SD card V30 (160 MBit/s reading) by [[Company:Samsung|Samsung]]<br/>'''Bottom:''' Bottom view showing SD card contacts
}}
{| class="wikitable" style="text-align: center;"
|+ Comparison of SD card Speed Class ratings<ref>{{Cite web |url=https://www.sdcard.org/developers/overview/speed_class/index.html |title=Speed Class |website=SD Association |access-date=2019-02-15}}</ref>
! scope="col" rowspan="2" | Minimum sequential<br/>writing speed
! rowspan="2" |Suggested<br/>max. bitrate
! scope="col" colspan="3" | Speed Class
! scope="col" colspan="4" | Video format{{Efn|The necessary recording and playback speed class requirements may vary by device.}}
|-
! scope="col" | Speed Class
! scope="col" | UHS Speed Class
! scope="col" | Video Speed Class 
! scope="col" | [[Engineering:Standard-definition television|SD]]
! scope="col" | [[Engineering:High-definition video|HD]] / Full HD
! scope="col" | [[4K resolution|4K]]
! scope="col" | [[8K resolution|8K]]
|-
! scope="row" | {{Nowrap|{{0|0}}2 MB/s}}
! {{0|0}}15 Mbit/s
| [[File:SDHC Speed Class 2.svg|frameless|upright=0.12]] {{Nowrap|Class 2 (C2)}}
| rowspan="3" {{N/a}} 
| rowspan="2" {{N/a}}  
| rowspan="7" {{Yes}}
| {{No}}
| rowspan="2" {{No}}
| rowspan="4" {{No}}
|-
! scope="row" | {{Nowrap|{{0|0}}4 MB/s}}
! {{0|0}}30 Mbit/s
| [[File:SDHC Speed Class 4.svg|frameless|upright=0.12]] {{Nowrap|Class 4 (C4)}} 
| rowspan="6" {{Yes}}
|-
! scope="row" | {{Nowrap|{{0|0}}6 MB/s}}
! {{0|0}}45 Mbit/s
| [[File:SDHC Speed Class 6.svg|frameless|upright=0.12]] {{Nowrap|Class 6 (C6)}}
| [[File:SD Video Speed Class 6.svg|frameless|upright=0.12]] {{Nowrap|Class 6 (V6)}}
| rowspan="5" {{Yes}}
|-
! scope="row" | {{Nowrap|10 MB/s}}
! {{0|0}}75 Mbit/s
| rowspan="4" | [[File:SD Class 10.svg|frameless|upright=0.12]] {{Nowrap|Class 10 (C10)}}
| [[File:SD UHS Speed Class 1.svg|frameless|upright=0.12]] {{Nowrap|Class 1 (U1)}}
| [[File:SD Video Speed Class 10.svg|frameless|upright=0.12]] {{Nowrap|Class 10 (V10)}}
|-
! scope="row" | {{Nowrap|30 MB/s}}
! 220 Mbit/s
| rowspan="3" | [[File:SD UHS Speed Class 3.svg|frameless|upright=0.12]] {{Nowrap|Class 3 (U3)}}
| [[File:SD Video Speed Class 30.svg|frameless|upright=0.12]] {{Nowrap|Class 30 (V30)}}
| rowspan="3" {{Yes}}
|-
! scope="row" | {{Nowrap|60 MB/s}}
! 460 Mbit/s
| [[File:SD Video Speed Class 60.svg|frameless|upright=0.12]] {{Nowrap|Class 60 (V60)}}
|-
! scope="row" | {{Nowrap|90 MB/s}}
! 700 Mbit/s
| [[File:SD Video Speed Class 90.svg|frameless|upright=0.12]] {{Nowrap|Class 90 (V90)}}
|}

==== Application Performance Class ====
''Application Performance Class'' is a newly defined standard from the SD Specification 5.1 and 6.0 which not only define sequential Writing Speeds but also mandates a minimum [[IOPS]] for reading and writing. Class A1 requires a minimum of 1,500 reading and 500 writing operations per second using 4 kbytes blocks, while class A2 requires 4,000 and 2,000 IOPS.<ref>"{{cite web|url=https://www.sdcard.org/downloads/pls/latest_whitepapers/Application_Peformance_Class_White_Paper.pdf |title=Application Performance Class: The new class of performance for applications on SD memory cards (SD 5.1)|website=sdcard.org|date= November 2016}}</ref> A2 class cards require host driver support as they use command queuing and write caching to achieve their higher speeds. Without they are guaranteed to at least reach A1 speeds. As of kernel 5.15, Linux fully supports A2.<ref>{{cite web |last=hominoid |title=Linux Supports A2 SDcards now! – ODROID |url=https://forum.odroid.com/viewtopic.php?t=44076 |website=ODROID by Hardkernel |publisher=ODROID |access-date=25 August 2023}}</ref>

{| class="wikitable" 
|+ Comparison of SD card Application Performance Class ratings<ref>{{Cite web|url=https://www.sdcard.org/developers/overview/application/index.html|title=Application&nbsp;Performance Class – SD Association|website=sdcard.org|access-date=2019-02-15}}</ref>
! rowspan="2" scope="col" | Name
! colspan="2" scope="col" | Minimum random [[IOPS]]
! rowspan="2" scope="col" | Minimum sustained<br/>sequential writing
|-
!Read
!Write
|-
! scope="row" | [[File:SD App Performance 1.svg|frameless|upright=0.2]] {{Nowrap|Application Performance Class 1 (A1)}}
| {{Nowrap|1500 [[IOPS]]}}
| {{Nowrap|{{0|0}}500 [[IOPS]]}}
| rowspan="2" |{{Nowrap|10 MB/s}}
|-
! scope="row" |[[File:SD App Performance 2.svg|frameless|upright=0.2]] {{Nowrap|Application Performance Class 2 (A2)}}
|{{Nowrap|4000 [[IOPS]]}}
|{{Nowrap|2000 [[IOPS]]}}
|}

==== "×" rating ====
{{main|Engineering:CD and DVD writing speed}}
{| class="wikitable" style="float:right; margin-left:1em;"
|-
! valign="top" | Rating
! valign="top" | Approx.<br/>(MB/s)
! valign="top" | Comparable<br/>speed class
|- style="text-align:center;"
| 16×
| 2.34
| [[File:SDHC Speed Class 2.svg|28px]] (13×)
|- style="text-align:center;"
| 32×
| 4.69
| [[File:SDHC Speed Class 4.svg|28px]] (27×)
|- style="text-align:center;"
| 48×
| 7.03
| [[File:SDHC Speed Class 6.svg|28px]] (40×)
|- style="text-align:center;"
| 100×
| 14.6
| [[File:SD Class 10.svg|28px]] (67×)
|}
The "×" rating, which was used by some card manufacturers and made obsolete by speed classes, is a multiple of the standard [[CD-ROM]] drive speed of 150&nbsp;KB/s{{efn|reference=1 KB = 1024 B}} (approximately 1.23&nbsp;Mbit/s). Basic cards transfer data at up to six times (6×) the CD-ROM speed; that is, 900&nbsp;kbit/s or 7.37&nbsp;Mbit/s. The 2.0 specification{{clarify|reason=which specification|date=September 2013}} defines speeds up to 200×, but is not as specific as Speed Classes are on how to measure speed. Manufacturers may report best-case speeds and may report the card's fastest read speed, which is typically faster than the write speed. Some vendors, including [[Company:Transcend Information|Transcend]] and Kingston, report their cards' write speed.<ref>{{cite web |url=http://www.kingston.com/us/flash/x-speed |title=Flash Memory Cards and X-Speed Ratings |publisher=Kingston |access-date=2017-08-05 |archive-date=2017-07-02 |archive-url=https://web.archive.org/web/20170702204220/http://www.kingston.com/us/flash/x-speed |url-status=dead }}</ref> When a card lists both a speed class and an "×" rating, the latter may be assumed a read speed only.{{citation needed|date=April 2018}}

===Real-world performance===
In applications that require sustained write throughput, such as video recording, the device might not perform satisfactorily if the SD card's class rating falls below a particular speed. For example, a high-definition [[Engineering:Camcorder|camcorder]] may require a card of not less than Class 6, suffering dropouts or corrupted video if a slower card is used. [[Engineering:Digital camera|Digital camera]]s with slow cards may take a noticeable time after taking a photograph before being ready for the next, while the camera writes the first picture.

The speed class rating does not totally characterize card performance. Different cards of the same class may vary considerably while meeting class specifications. A card's speed depends on many factors, including:
* The frequency of soft errors that the card's controller must re-try
* [[Engineering:Write amplification|Write amplification]]: The flash controller may need to overwrite more data than requested. This has to do with performing read-modify-write operations on write blocks, freeing up (the much larger) erase blocks, while moving data around to achieve [[Wear leveling|wear leveling]].
* File fragmentation: where there is not sufficient space for a file to be recorded in a contiguous region, it is split into non-contiguous fragments. This does not cause rotational or head-movement delays as with electromechanical hard drives, but may decrease speed⁠—for instance, by requiring additional reads and computation to determine where on the card the file's next fragment is stored.

In addition, speed may vary markedly between writing a large amount of data to a single file ([[Sequential access|sequential access]], as when a [[Engineering:Digital camera|digital camera]] records large photographs or videos) and writing a large number of small files (a [[Random access|random-access]] use common in [[Engineering:Smartphone|smartphone]]s). A study in 2012 found that, in this random-access use, some Class 2 cards achieved a write speed of 1.38&nbsp;MB/s, while all cards tested of Class 6 or greater (and some of lower Classes; lower Class does not ''necessarily'' mean better small-file performance), including those from major manufacturers, were over 100 times slower.<ref name=necstudy/> In 2014, a blogger measured a 300-fold performance difference on small writes; this time, the best card in this category was a class 4 card.<ref name=Gough2014/>

==Features==
===Card security===

====Commands to disable writes====
The host device can command the SD card to become read-only (to reject subsequent commands to write information to it). There are both reversible and irreversible host commands that achieve this.<ref>{{Cite web |last=By |date=2014-01-19 |title=The Tiniest SD Card Locker |url=https://hackaday.com/2014/01/18/the-tiniest-sd-card-locker/ |access-date=2023-01-20 |website=Hackaday |language=en-US}}</ref><ref>{{cite patent |country=US |number=7827370 |status=patent}}</ref>

====Write-protect notch====
[[File:SD card unlocked and locked.svg|thumb|Unlocked and locked SD cards]]
[[File:Vorderseite Sony Tough SF-M64T SDUHSII011CORRklein.png|thumb|Sony 64GB SF-M Tough Series UHS-II SDXC Memory Card is one of the few cards in the market without a sliding tab on the write protect notch.]]

Most full-size SD cards have a "mechanical write protect switch" allowing the user to advise the host computer that the user wants the device to be treated as read-only. This does not protect the data on the card if the host is compromised: "It is the responsibility of the host to protect the card. The position [i.e., setting] of the write protect switch is unknown to the internal circuitry of the card."<ref>{{Cite web|url=https://www.sdcard.org/downloads/pls/index.html|title=Simplified Specifications – SD Association, version 3.10, Part 1, Physical Layer, section 4.3.6" Write Protect Management"|website=sdcard.org|access-date=2019-04-11}}</ref> Some host devices do not support write protection, which is an optional feature of the SD specification, and drivers and devices that do obey a read-only indication may give the user a way to override it.{{cn|date=September 2023}}

The switch is a sliding tab that covers a notch in the card. The miniSD and microSD formats do not directly support a write protection notch, but they can be inserted into full-size adapters which do.{{cn|date=September 2023}}

When looking at the SD card from the top, the right side (the side with the beveled corner) must be notched.{{cn|date=September 2023}}

On the left side, there may be a write-protection notch. If the notch is omitted, the card can be read and written. If the card is notched, it is read-only. If the card has a notch and a sliding tab which covers the notch, the user can slide the tab upward (toward the contacts) to declare the card read/write, or downward to declare it read-only.{{cn|date=September 2023}} The diagram to the right shows an orange sliding write-protect tab in both the unlocked and locked positions.{{cn|date=September 2023}}

Cards sold with content that must not be altered are permanently marked read-only by having a notch and no sliding tab.{{cn|date=September 2023}}

====Card password====
[[File:Sdadaptersandcards.jpg|thumb|MicroSD-to-SD adapter (left), microSD-to-miniSD adapter (middle), microSD card (right)]]

A host device can lock an SD card using a password of up to 16&nbsp;bytes, typically supplied by the user.{{cn|date=September 2023}} A locked card interacts normally with the host device except that it rejects commands to read and write data.{{cn|date=September 2023}} A locked card can be unlocked only by providing the same password. The host device can, after supplying the old password, specify a new password or disable locking. Without the password (typically, in the case that the user forgets the password), the host device can command the card to erase all the data on the card for future re-use (except card data under DRM), but there is no way to gain access to the existing data.{{cn|date=September 2023}}

[[Software:Windows Phone 7|Windows Phone 7]] devices use SD cards designed for access only by the phone manufacturer or mobile provider. An SD card inserted into the phone underneath the battery compartment becomes locked "to the phone with an automatically generated key" so that "the SD card cannot be read by another phone, device, or PC".<ref>{{Cite web|url=https://support.microsoft.com/en-us/windows/windows-phone-7-3ebc303c-59c0-d367-3995-f258b184fabb|title=Windows Phone 7 – Microsoft Support|website=support.microsoft.com}}</ref> Symbian devices, however, are some of the few that can perform the necessary low-level format operations on locked SD cards. It is therefore possible to use a device such as the [[Engineering:Nokia N8|Nokia N8]] to reformat the card for subsequent use in other devices.<ref>{{Cite web|url=https://www.engadget.com/2010/11/17/windows-phone-7s-microsd-mess-the-full-story-and-how-nokia-ca/|title=Windows Phone 7's microSD mess: the full story (and how Nokia can help you out of it)|website=Engadget}}</ref>

===smartSD cards===
A smartSD memory card is a microSD card with an internal "[[Secure element|secure element]]" that allows the transfer of ISO 7816 [[Smart card application protocol data unit|Application Protocol Data Unit]] commands to, for example, JavaCard applets running on the internal secure element through the SD bus.<ref>{{cite web |url=https://www.sdcard.org/downloads/pls/latest_whitepapers/Activating_New_Mobile_Services_and_Business_Models_With_smartSD_Memory_Cards_Revsied_11-3-2014.pdf |title=Activating New Mobile Services and Business Models with smartSD Memory cards |date=November 2014 |publisher=SD Association |access-date=2017-08-02 |archive-date=2016-12-23 |archive-url=https://web.archive.org/web/20161223213554/https://www.sdcard.org/downloads/pls/latest_whitepapers/Activating_New_Mobile_Services_and_Business_Models_With_smartSD_Memory_Cards_Revsied_11-3-2014.pdf |url-status=dead }}</ref>

Some of the earliest versions of microSD memory cards with secure elements were developed in 2009 by DeviceFidelity, Inc.,<ref>{{cite web |url=https://www.nfcw.com/2009/11/11/32254/devicefidelity-launches-low-cost-microsd-based-nfc-solution/ |title=DeviceFidelity launches low cost microSD-based NFC solution |website=nfcw.com |last=Clark |first=Sarah |date=11 November 2009 |access-date=28 July 2021 }}</ref><ref>{{cite web |url=https://www.secureidnews.com/news-item/devicefidelity-rolls-out-microsd-payment-tool/ |title=DeviceFidelity rolls out microSD payment tool |website=SecureIDNews |date=10 November 2009 |access-date=28 July 2021 }}</ref> a pioneer in [[Near-field communication|near-field communication]] (NFC) and mobile payments, with the introduction of In2Pay and CredenSE products, later commercialized and certified for mobile contactless transactions by [[Company:Visa Inc.|Visa]] in 2010.<ref>{{cite web |url=https://investor.visa.com/news/news-details/2010/Visa-and-DeviceFidelity-Collaborate-to-Accelerate-Adoption-of-Mobile-Contactless-Payments/default.aspx |title=Visa and DeviceFidelity Collaborate to Accelerate Adoption of Mobile Contactless Payments |website=visa.com |date=15 February 2010 |access-date=28 July 2021 }}</ref> DeviceFidelity also adapted the In2Pay microSD to work with the Apple iPhone using the iCaisse, and pioneered the first NFC transactions and mobile payments on an Apple device in 2010.<ref>{{cite web |url=https://www.engadget.com/2010-05-18-in2pay-is-the-name-of-visa-and-devicefidelitys-money-grubbing-i.html |title=In2Pay is the name of Visa and DeviceFidelity's money-grubbing iPhone case |website=Engadget |date=18 May 2010 |access-date=28 July 2021 }}</ref><ref>{{cite web |url=https://www.youtube.com/watch?v=trHueSWx0-g | archive-url=https://ghostarchive.org/varchive/youtube/20211029/trHueSWx0-g| archive-date=2021-10-29|title=Device Fidelity's Amitaabh Mohortra Speaks about their micro NFC device for almost any phone |website=youtube.com |date=26 October 2013 |access-date=28 July 2021 |url-status=live}}{{cbignore}}</ref><ref>{{cite web |url=https://www.nfcw.com/2010/09/23/34489/devicefidelity-adds-nfc-microsd-support-for-iphone-4/ |title=DeviceFidelity adds NFC microSD support for iPhone 4 |last=Clark |first=Mike |website=nfcw.com |date=23 September 2010 |access-date=28 July 2021 }}</ref>

Various implementations of smartSD cards have been done for payment applications and secured authentication.<ref>{{cite web|url=http://www.sdcard.org/developers/overview/ASSD/smartsd|title=smartSD Memory Cards|publisher=SD Association|access-date=2016-02-23}}</ref><ref>{{cite web|url=http://nfctimes.com/news/microsd-vendor-announces-taiwanese-m-payment-trial-using-htc-nfc-phones|title=MicroSD Vendor Announces Taiwanese M-Payment Trial Using HTC NFC Phones |publisher=NFC Times|access-date=2016-02-23}}</ref> In 2012 [[Company:Good Technology|Good Technology]] partnered with DeviceFidelity to use microSD cards with secure elements for mobile identity and [[Access control|access control]].<ref>{{cite web |url=https://www.secureidnews.com/news-item/devicefidelitys-good-vault-provides-identity-and-access-solution-for-ios/ |title=DeviceFidelity's Good Vault provides identity and access solution for iOS |website=SecureIDNews |last=Hudson |first=Andrew |date=10 December 2012 |access-date=28 July 2021 }}</ref>

microSD cards with Secure Elements and NFC ([[Near-field communication|near-field communication]]) support are used for mobile payments, and have been used in direct-to-consumer mobile wallets and mobile banking solutions, some of which were launched by major banks around the world, including [[Company:Bank of America|Bank of America]], US Bank and Wells Fargo,<ref>{{cite press release |url=https://www.businesswire.com/news/home/20130114005951/en/Datacard-Group-DeviceFidelity-U.S.-Bank-Announce-New |title=Datacard Group, DeviceFidelity and U.S. Bank Announce New Smart Card and Mobile Payment Program |publisher=Datacard Group |date=14 January 2013 |access-date=28 July 2021 |via=Businesswire }}</ref><ref>{{cite web |url=https://www.nfcw.com/2010/08/19/34339/bank-of-america-to-run-nfc-payments-trial-in-new-york/ |title=Bank of America to run NFC payments trial in New York |website=nfcw.com |last=Clark |first=Sarah |date=19 August 2010 |access-date=28 July 2021 }}</ref><ref>{{Cite web |url=https://www.businesswire.com/news/home/20101206007176/en/Wells-Fargo-Roll-Mobile-Payments-Pilot-Visa |title=Wells Fargo to Roll Out Mobile Payments Pilot; Visa Demonstrating Capability at CARTES 2010 &#124; Business Wire |access-date=2020-10-14 |archive-date=2020-10-14 |archive-url=https://web.archive.org/web/20201014173430/https://www.businesswire.com/news/home/20101206007176/en/Wells-Fargo-Roll-Mobile-Payments-Pilot-Visa |url-status=dead }}</ref> while others were part of innovative new direct-to-consumer [[Finance:Neobank|neobank]] programs such as moneto, first launched in 2012.<ref>{{cite press release |url=https://www.prweb.com/releases/2012/1/prweb9086910.htm |title=DeviceFidelity and SpringCard Launch moneto, the World's First Multi-Platform Mobile Wallet for iPhone and Android at CES |publisher=DeviceFidelity |date=10 January 2012 |access-date=28 July 2021 |via=Cision}}</ref><ref>{{cite web |url=https://www.nfcw.com/2012/09/11/317791/moneto-to-bring-nfc-payments-to-europe/ |title=Moneto to bring NFC payments to Europe |website=nfcw.com |last=Clark |first=Sarah |date=11 September 2012 |access-date=28 July 2021 }}</ref><ref>{{cite web|url=http://www.rfid-ready.com/201403038507/garanti-bank-deploys-nfc-services-on-microsd.html|title=Garanti Bank deploys NFC services on microSD|publisher=RFID Ready|access-date=2016-02-23|archive-date=2017-02-02|archive-url=https://web.archive.org/web/20170202124458/http://www.rfid-ready.com/201403038507/garanti-bank-deploys-nfc-services-on-microsd.html|url-status=dead}}</ref><ref>{{cite web|url=http://www.nfcworld.com/2012/10/31/320843/devicefidelity-launches-new-range-of-nfc-microsd-devices/|title=DeviceFidelity launches new range of NFC microSD devices |publisher=NFC World+|date=2012-10-31|access-date=2016-02-23}}</ref>

microSD cards with Secure Elements have also been used for secure voice encryption on mobile devices, which allows for one of the highest levels of security in person-to-person voice communications.<ref>{{cite web |url=https://koolspan.com/iphone_devicefidelity/ |title=iPhone Voice Encryption from KoolSpan and DeviceFidelity |website=koolspan.com |date=11 March 2013 |access-date=28 July 2021 }}</ref> Such solutions are heavily used in intelligence and security.

In 2011, HID Global partnered with [[Organization:Arizona State University|Arizona State University]] to launch campus access solutions for students using microSD with Secure Element and MiFare technology provided by DeviceFidelity, Inc.<ref>{{cite web |url=https://www.cr80news.com/news-item/arizona-students-first-to-trial-mobile-phones-with-nfc-for-door-access/ |title=Arizona students first to trial mobile phones with NFC for door access |work=CR80 News |last=Corum |first=Chris |date=14 September 2011 |access-date=28 July 2021 }}</ref><ref>{{cite web |url=https://www.youtube.com/watch?v=d4NmYdMAAHU | archive-url=https://ghostarchive.org/varchive/youtube/20211029/d4NmYdMAAHU| archive-date=2021-10-29|title=Case Study: Mobile Access Pilot at Arizona State University |website=youtube.com |date=14 October 2011 |access-date=28 July 2021 |url-status=live}}{{cbignore}}</ref> This was the first time regular mobile phones could be used to open doors without need for electronic access keys.

===<span class="anchor" id="Integrated Wi-Fi"></span> Vendor enhancements===
 {{multiple image
 | SD cards with integrated Wi-Fi
 | perrow      = 2
 | total_width = 390
 | image1      = Eye-Fi Wifi Card.jpg
 | caption1    = Eye-Fi Mobi 16&nbsp;GB
 | image2      = FlashAir 014 (15247275839) (cropped).jpg
 | caption2    = Toshiba FlashAir 16&nbsp;GB
 | image3      = Pqi-air-card 開箱 (8536928274) (cropped).jpg
 | caption3    = PQI air card 4 GB
 | image4      = Transcend WiFi SD-Card.jpg
 | caption4    = Transcend Wi-Fi 16 GB
 }}
[[File:USB-SD-Cards.jpg|thumb|SD cards with dual interfaces: SD and USB]]

Vendors have sought to differentiate their products in the market through various vendor-specific features:
* '''Integrated [[Wi-Fi]]''' – Several companies produce SD cards with built-in Wi-Fi transceivers supporting static security (WEP 40; 104; and 128, WPA-PSK and WPA2-PSK). The card lets any digital camera with an SD slot transmit captured images over a wireless network, or store the images on the card's memory until it is in range of a wireless network. Examples include: [[Company:Eye-Fi|Eye-Fi]] / SanDisk, Transcend Wi-Fi, Toshiba FlashAir, Trek Flucard, PQI Air Card and LZeal ez Share.<ref>{{cite web |url=http://www.eye.fi/ |title=Eye-Fi |access-date=2010-08-22 |url-status=dead |archive-url=http://webarchive.loc.gov/all/20100826002041/http%3A//www.eye.fi/ |archive-date=2010-08-26 }}</ref> Some models [[Engineering:Geotagging|geotag]] their pictures.
* '''Pre-loaded content''' – In 2006, SanDisk announced [[Gruvi]], a microSD card with extra digital rights management features, which they intended as a medium for publishing content. SanDisk again announced pre-loaded cards in 2008, under the [[SlotMusic|slotMusic]] name, this time not using any of the DRM capabilities of the SD card.<ref>{{cite web|last=Robson |first=Wayde |url=http://www.audioholics.com/news/industry-news/sandisk-slotmusic |title=AudioHolics |publisher=AudioHolics |access-date=2014-01-02}}</ref> In 2011, SanDisk offered various collections of 1000 songs on a single slotMusic card for about $40,<ref>{{cite web|url=http://www.sandisk.com/consumer-products/slotradio|title=slotRadio|publisher=SanDisk |access-date= 2011-11-27}}</ref> now restricted to compatible devices and without the ability to copy the files.
* '''Integrated USB connector''' – The [[Company:SanDisk|SanDisk]] '''SD Plus''' product can be plugged directly into a [[Engineering:USB|USB]] port without needing a USB card reader.<ref>{{Citation | url = https://www.theregister.co.uk/2005/07/25/review_sandisk_ultra_ii_sd_plus/ | title = SanDisk Ultra II SD Plus USB/SD card | newspaper = The Register | place = {{wipe|United Kingdom}} | date = 2005-07-25}}</ref> Other companies introduced comparable products, such as the '''Duo SD''' product of OCZ Technology and the '''3 Way''' (microSDHC, SDHC and USB) product of A-DATA, which was available in 2008 only.
* '''Different colors''' – SanDisk has used various colors of plastic or adhesive label, including a "gaming" line in translucent plastic colors that indicated the card's capacity.
* '''Integrated display''' – In 2006, A-DATA announced a '''Super Info SD''' card with a digital display that provided a two-character label and showed the amount of unused memory on the card.<ref>{{cite web|url=http://www.techpowerup.com/reviews/AData/ADATASuperInfoSD/ |title= A-DATA Super Info SD Card 512MB |publisher= Tech power up |date=2007-02-20 |access-date=2011-12-30}}</ref>

===SDIO cards===
[[File:SDIO Vector.svg|thumb]]
[[File:HP PhotoSmart SDIO Kamera.jpg|thumb|Camera using the SDIO interface to connect to some HP iPAQ devices]]

A SDIO (Secure Digital Input Output) card is an extension of the SD specification to cover I/O functions. SDIO cards are only fully functional in host devices designed to support their input-output functions (typically PDAs like the [[Engineering:Palm Treo|Palm Treo]], but occasionally laptops or mobile phones).{{cn|date=September 2023}} These devices can use the SD slot to support [[Engineering:GPS|GPS]] receivers, [[Modem|modem]]s, [[Barcode reader|barcode reader]]s, FM radio tuners, TV tuners, RFID readers, [[Engineering:Digital camera|digital camera]]s and interfaces to [[Wi-Fi]], [[Bluetooth]], [[Ethernet]] and IrDA. Many other SDIO devices have been proposed, but it is now more common for I/O devices to connect using the USB interface.{{cn|date=September 2023}}

SDIO cards support most of the memory commands of SD cards. SDIO cards can be structured as eight logical cards, although currently, the typical way that an SDIO card uses this capability is to structure itself as one I/O card and one memory card.{{cn|date=September 2023}}

The SDIO and SD interfaces are mechanically and electrically identical. Host devices built for SDIO cards generally accept SD memory cards without I/O functions. However, the reverse is not true, because host devices need suitable drivers and applications to support the card's I/O functions. For example, an HP SDIO camera usually does not work with PDAs that do not list it as an accessory. Inserting an SDIO card into any SD slot causes no physical damage nor disruption to the host device, but users may be frustrated that the SDIO card does not function fully when inserted into a seemingly compatible slot. (USB and Bluetooth devices exhibit comparable compatibility issues, although to a lesser extent thanks to standardized [[Software:Class driver|USB device classes]] and Bluetooth profiles.){{cn|date=September 2023}}

The SDIO family comprises Low-Speed and Full-Speed cards. Both types of SDIO cards support SPI and one-bit SD bus types. Low-Speed SDIO cards are allowed to also support the four-bit SD bus; Full-Speed SDIO cards are required to support the four-bit SD bus. To use an SDIO card as a "combo card" (for both memory and I/O), the host device must first select four-bit SD bus operation. Two other unique features of Low-Speed SDIO are a maximum clock rate of 400&nbsp;kHz for all communications, and the use of Pin 8 as "interrupt" to try to initiate dialogue with the host device.<ref name="SDIOspec">{{cite web|url=https://www.sdcard.org/developers/overview/sdio/sdio_spec/|title=Simplified Version of SDIO CARD SPEC|publisher=SD Association|access-date=2011-12-09|archive-date=2015-04-15|archive-url=https://web.archive.org/web/20150415230526/https://www.sdcard.org/developers/overview/sdio/sdio_spec/|url-status=dead}}</ref>

===Compatibility===
[[File:Stream64i.jpg|thumb|{{nowrap|Wi-Fi}}/DAB+/FM/CD/MP3/WMA/USB/SDHC/podcast stereo recorder with [[Engineering:IPod|iPod]] dock]]
Host devices that comply with newer versions of the specification provide [[Backward compatibility|backward compatibility]] and accept older SD cards.<ref name="sdcard.org"/> For example, SDXC host devices accept all previous families of SD memory cards, and SDHC host devices also accept standard SD cards.

Older host devices generally do not support newer card formats, and even when they might support the bus interface used by the card,<ref name=sdcard_using_sdxc/> there are several factors that arise:
* A newer card may offer greater capacity than the host device can handle (over 4&nbsp;GB for SDHC, over 32&nbsp;GB for SDXC).
* A newer card may use a file system the host device cannot navigate ([[FAT32]] for SDHC, [[ExFAT|exFAT]] for SDXC)
* Use of an SDIO card requires the host device be designed for the input/output functions the card provides.
* The hardware interface of the card was changed starting with the version 2.0 (new high-speed bus clocks, redefinition of storage capacity bits) and SDHC family (ultra-high speed (UHS) bus)
* UHS-II has physically more pins but is backwards compatible to UHS-I and non-UHS for both slot and card.<ref name="sda_bus_speed"/>
* Some vendors produced SDSC cards above 1&nbsp;GB before the SDA had standardized a method of doing so.

{| class="wikitable"
|+ SD compatibility table
! scope="col" | SDSC
! scope="col" | SDHC
! scope="col" | SDHC<br/>UHS
! scope="col" | SDXC
! scope="col" | SDXC<br/>UHS 
! scope="col" | SDIO
|- 
! style="text-align:left;" | SDSC
| {{Partial}}{{Efn|name=sdsccompat|See discussion about storage capacity and compatibilities.}} || {{Partial|FAT16, < 4&nbsp;GB}}{{Efn|name=sdsccompat}} || {{Partial|FAT16, < 4&nbsp;GB}}{{Efn|name=sdsccompat}} || {{No}} || {{No}} || {{No}}
|-
! style="text-align:left;" | SDHC
| {{Yes}} || {{Yes}} || {{good|In non-UHS mode}} || {{Partial|FAT32}} || {{Partial|FAT32 in non-UHS mode}} || {{No}}
|-
! style="text-align:left;" | SDHC UHS
| {{good|In non-UHS mode}} || {{good|In non-UHS mode}} ||  {{Yes|In UHS mode}} || {{Partial|FAT32 in non-UHS mode}} || {{Partial|FAT32 in UHS mode}} ||  {{No}}
|- 
! style="text-align:left;" | SDXC
| {{Yes}} || {{Yes}} || {{good|In non-UHS mode}} || {{Yes}} || {{good|In non-UHS mode}} || {{No}}
|- 
! style="text-align:left;" | SDXC UHS
| {{good|In non-UHS mode}} || {{good|In non-UHS mode}} ||  {{Yes|In UHS mode}} || {{good|In non-UHS mode}}|| {{Yes|In UHS mode}} || {{No}}
|-
! style="text-align:left;" | SDIO
| {{partial|Varies}} ||  {{partial|Varies}} || {{partial|Varies}} || {{partial|Varies}} || {{partial|Varies}} || {{Yes}}
|}

==Markets==
[[File:Micro-SD-Kartenleser der Nintendo Switch 20230405 HOF09182 RAW-Export.png|thumb|alt=This image shows an internal MicroSD card reader, as it can be found in game consoles like the Nintendo Switch|An internal microSD card reader, taken from a [[Engineering:Nintendo Switch|Nintendo Switch]]]]
Due to their compact size, Secure Digital cards are used in many consumer electronic devices, and have become a widespread means of storing several gigabytes of data in a small size. Devices in which the user may remove and replace cards often, such as [[Engineering:Digital camera|digital camera]]s, [[Engineering:Camcorder|camcorder]]s and [[Engineering:Video game console|video game console]]s, tend to use full-sized cards. Devices in which small size is paramount, such as [[Engineering:Mobile phone|mobile phone]]s, action cameras such as the [[Company:GoPro#HERO cameras|GoPro Hero]] series, and [[Engineering:Unmanned aerial vehicle|camera drones]], tend to use microSD cards.<ref>{{cite web |title=4 Features and Benefits of a Micro SD Transflash Memory Card – Steve's Digicams |url=http://www.steves-digicams.com/knowledge-center/how-tos/photo-accessories/4-features-and-benefits-of-a-micro-sd-transflash-memory-card.html |website=steves-digicams.com}}</ref><ref>{{cite web |title=Advantages and Disadvantages of Memory Cards |url=https://www.engadget.com/2016-10-11-advantages-and-disadvantages-of-memory-cards.html |website=Engadget |language=en |date=2016-10-11 |access-date=2020-11-30 |archive-date=2020-10-28 |archive-url=https://web.archive.org/web/20201028124543/https://www.engadget.com/2016-10-11-advantages-and-disadvantages-of-memory-cards.html |url-status=dead }}</ref>

=== Mobile phones ===
The microSD card has helped propel the smartphone market by giving both manufacturers and consumers greater flexibility and freedom.

While [[Cloud storage|cloud storage]] depends on stable internet connection and sufficiently voluminous data plans, memory cards in mobile devices provide location-independent and [[Privacy|private]] storage expansion with much higher transfer rates and no [[Network delay|network delay]], enabling applications such as [[Photography|photography]] and video recording. While data stored internally on [[Engineering:Brick (electronics)|bricked device]]s is [[Data loss|inaccessible]], data stored on the memory card can be salvaged and accessed externally by the user as [[Mass storage|mass storage]] device. A benefit over USB on the go storage expansion is uncompromised ergonomy. The usage of a memory card also protects the mobile phone's non-replaceable internal storage from weardown from heavy applications such as excessive camera usage and portable [[FTP server]] hosting over WiFi Direct. Due to the technical development of memory cards, users of existing mobile devices are able to expand their storage further and priceworthier with time.<ref>{{cite web |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-nz/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |website=ni.com |language=en |date=2020-07-23}}</ref><ref>{{cite web |title=12 Advantages & Disadvantages of Using SD Card in Smartphone |url=https://www.datanumen.com/blogs/12-advantages-disadvantages-using-sd-card-smartphone/ |website=Data Recovery Blog |date=23 November 2017}}</ref><ref>{{cite web |last=Ali |first=Mudassar |title=Benefits of Using an SD Card |url=https://medium.com/@mudassarali143/benefits-of-using-an-sd-card-fc9f3e477e05 |website=Medium |language=en |date=27 November 2018}}</ref>

Recent versions of major operating systems such as [[Software:Windows Mobile|Windows Mobile]] and [[Software:Android (operating system)|Android]] allow applications to run from microSD cards, creating possibilities for new usage models for SD cards in mobile computing markets, as well as clearing available internal storage space.<ref>{{cite web|url=http://www.androidcentral.com/inside-marshmallow-adoptable-storage|title=Inside Marshmallow: Adoptable storage |publisher=Android Central|date=2015-11-15|access-date=2016-02-23}}</ref>

SD cards are not the most economical solution in devices that need only a small amount of non-volatile memory, such as station presets in small radios. They may also not present the best choice for applications that require higher storage capacities or speeds as provided by other flash card standards such as [[CompactFlash]]. These limitations may be addressed by evolving memory technologies, such as the new SD 7.0 specifications which allow storage capabilities of up to 128 TB.{{efn|name="here, 1 TB = 1024"}}<ref>{{cite web |url=https://www.sdcard.org/consumers/choices/speed_class/index.html |title=Speed Class Standards for Video Recording|website=SD Association |access-date=21 November 2018}}</ref>

Many personal computers of all types, including tablets and mobile phones, use SD cards, either through built-in slots or through an active electronic adapter. Adapters exist for the PC card, ExpressBus, [[Engineering:USB|USB]], FireWire and the [[Parallel port|parallel printer port]]. Active adapters also let SD cards be used in devices designed for other formats, such as [[CompactFlash]]. The [[Company:FlashPath|FlashPath]] adapter lets SD cards be used in a [[Floppy disk|floppy disk]] drive.

Some devices such as the [[Engineering:Samsung Galaxy Fit (smartphone)|Samsung Galaxy Fit]] (2011) and [[Engineering:Samsung Galaxy Note 8.0|Samsung Galaxy Note 8.0]] (2013) have an SD card compartment located externally and accessible by hand, while it is located under the battery cover on other devices. More recent mobile phones use a pin-hole ejection system for the tray which houses both the memory card and [[SIM card]].

===Counterfeits===
[[File:Samsung Pro 64gb micro-SDXC original and falsification front and back.jpg|thumb|[[Company:Samsung Electronics|Samsung]] Pro 64&nbsp;GB microSDXC original (left) and counterfeit (right): The counterfeit claims to have 64&nbsp;GB in capacity, but only 8&nbsp;GB (Class 4 speed) are usable: When trying to write more than 8 GB, [[Data loss|data loss]] occurs. Also used for SanDisk 64&nbsp;GB fakes.]]
[[File:Decapsulated microSD memory card lineup-genuine, questionable, and fake-counterfeit.jpg|thumb|Images of genuine, questionable and counterfeit microSD (Secure Digital) cards before and after decapsulation. Details [http://www.bunniestudios.com/blog/?page_id=1022 at source], photo by Andrew Huang]]

Commonly found on the market are mislabeled or counterfeit Secure Digital cards that report a fake capacity or run slower than labeled.<ref>{{cite web |last=bunnie |title=On MicroSD Problems |url=https://www.bunniestudios.com/blog/?page_id=1022 |access-date=2024-01-22 |website=bunniestudios.com}}</ref><ref name="c't2007">{{cite web |last=Schnurer |first=Georg |title=Gefälschte SD-Karten |language=de |trans-title=Fake SD-cards |publisher=Heise mobile – c't magazin für computertechnik |date=2007-02-28 |url=http://www.heise.de/mobil/meldung/Gefaelschte-SD-Karten-151283.html |access-date=2013-06-07 |archive-date=2013-06-23 |archive-url=https://web.archive.org/web/20130623055703/http://www.heise.de/mobil/meldung/Gefaelschte-SD-Karten-151283.html |url-status=dead }}</ref><ref name="c't2013-häufiges">{{cite web |url= http://www.heise.de/mobil/meldung/Smartphones-waehlerisch-bei-microSDHC-Karten-1825259.html |title=Smartphones wählerisch bei microSDHC-Karten |publisher=Heise mobile – c't magazin für computertechnik |date=2013-03-18 |access-date=2013-06-09 |last=Feddern |first=Boi |language=de}}</ref>
Software tools exist to check and detect [[Engineering:USB flash drive#Counterfeit products|counterfeit products]].<ref name="h2testw">{{cite web
|title=H2testw heise Download |language=de
|url=https://www.heise.de/download/product/h2testw-50539
|access-date=2016-11-26}}</ref><ref name="f3">{{cite web
|title=F3 by Digirati
|url=http://oss.digirati.com.br/f3/
|access-date=2016-11-26}}</ref> Detection of counterfeit cards usually involves copying files with random data to the SD card until the card's capacity is reached, and copying them back. The files that were copied back can be tested either by comparing checksums (e.g. [[Software:Md5sum|MD5]]), or trying to [[Data compression|compress]] them. The latter approach leverages the fact that counterfeited cards let the user read back files, which then consist of easily compressible uniform data (for example, repeating 0xFFs).

===Digital cameras===
[[File:Pentax K10D with SanDiskSD card.jpg|thumb|SD card in a DSLR camera]]

Secure Digital memory cards can be used in Sony [[Engineering:XDCAM|XDCAM]] EX [[Engineering:Camcorder|camcorder]]s with an adapter.<ref>{{cite web|url=http://pro.sony.com/bbsc/ssr/micro-xdcamexsite/cat-accessories/product-MEADSD01/ |title=MEAD-SD01 SDHC card adapter (Sony) |publisher=Pro.sony.com |access-date=2014-01-02}}</ref>

===Personal computers===
Although many [[Engineering:Personal computer|personal computer]]s accommodate SD cards as an auxiliary storage device using a built-in slot, or can accommodate SD cards by means of a USB adapter, SD cards cannot be used as the primary hard disk through the onboard ATA controller, because none of the SD card variants support ATA signalling. Primary hard disk use requires a separate SD host controller<ref>{{cite web|url=http://www.embeddedarm.com/products/board-detail.php?product=TS-7800 |title=TS-7800 Embedded |publisher=Embeddedarm.com |access-date=2010-08-22}}</ref> or an SD-to-CompactFlash converter. However, on computers that support bootstrapping from a USB interface, an SD card in a USB adapter can be the boot disk, provided it contains an operating system that supports USB access once the bootstrap is complete.

In [[Engineering:Laptop|laptop]] and [[Engineering:Tablet computer|tablet computer]]s, memory cards in an integrated [[Memory card reader|memory card reader]] offer an ergonomical benefit over USB [[Flash drive|flash drive]]s, as the latter sticks out of the device, and the user would need to be cautious not to bump it while transporting the device, which could damage the USB port. Memory cards have a unified shape and do not reserve a USB port when inserted into a computer's dedicated card slot.

Since late 2009, newer [[Company:Apple Inc.|Apple]] computers with installed SD card readers have been able to boot in [[Software:MacOS|macOS]] from SD storage devices, when properly formatted to [[HFS Plus|Mac OS Extended]] file format and the default partition table set to [[GUID Partition Table]].<ref>{{cite web|url=http://support.apple.com/kb/HT3553 |title=About the SD and SDXC card slot |publisher=Support.apple.com |date=2013-06-08 |access-date=2013-11-13}}</ref> 

SD cards are increasing in usage and popularity among owners of [[Vintage computer|vintage computer]]s like [[Engineering:Atari 8-bit family|8-bit Atari]]. For example SIO2SD ([[Atari SIO|SIO]] is an Atari port for connecting external devices) is used nowadays. Software for an 8-bit Atari may be included on one SD card that may have less than 4–8 GB of disk size (2019).<ref>{{Cite web|url=https://retrohax.net/sio2sd-for-atari/|title=SIO2SD for 8-bit Atari|date=May 9, 2016}}</ref>

===Embedded systems===
[[File:Arduino Ethernet Shield (pre-production sample).jpg|thumb|A shield (daughterboard) that gives Arduino prototyping microprocessors access to SD cards]]

In 2008, the SDA specified Embedded SD, "leverag[ing] well-known SD standards" to enable non-removable SD-style devices on printed circuit boards.<ref>{{cite web|title=Embedded SD|publisher=SD Association|url=http://www.sdcard.org/developers/overview/embedded_sd/|access-date=2011-11-30}}</ref> However this standard was not adopted by the market while the MMC standard became the de facto standard for embedded systems. SanDisk provides such embedded memory components under the iNAND brand.<ref>{{cite web|title=iNAND Embedded Flash Drives|publisher=SanDisk|url=http://www.sandisk.com/business-solutions/inand-embedded-flash-drives|access-date=2011-11-30}}</ref>

Most modern [[Engineering:Microcontroller|microcontroller]]s have built-in SPI logic that can interface to an SD card operating in its SPI mode, providing non-volatile storage. Even if a microcontroller lacks the SPI feature, the feature can be emulated by [[Bit banging|bit banging]]. For example, a home-brew hack combines spare General Purpose Input/Output (GPIO) pins of the processor of the [[Company:Linksys|Linksys]] WRT54G router with MMC support code from the [[Software:Linux kernel|Linux kernel]].<ref>{{cite web|url=http://www.dd-wrt.com/wiki/index.php/Linksys_WRT54G-TM_SD/MMC_mod |title=Linksys WRT54G-TM SD/MMC mod – DD-WRT Wiki |publisher=Dd-wrt.com |date=2010-02-22 |access-date=2010-08-22}}</ref> This technique can achieve throughput of up to {{Nowrap|1.6 Mbit/s}}.

===Music distribution===
Prerecorded microSDs have been used to commercialize music under the brands [[SlotMusic|slotMusic]] and [[SlotRadio|slotRadio]] by [[Company:SanDisk|SanDisk]] and MQS by Astell & Kern.

==Technical details==
{{multiple image
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 | image2 = SD card adapters.jpg
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}}

===<span class="anchor" id="Physical size"></span>Physical size===
The SD card specification defines three physical sizes. The SD and SDHC families are available in all three sizes, but the SDXC and SDUC families are not available in the mini size, and the SDIO family is not available in the micro size. Smaller cards are usable in larger slots through use of a passive adapter.

====Standard====
[[File:MicroSD MemoryCard 002.jpg|thumb|upright|Size comparison of families: SD (blue), miniSD (green), microSD (red)]]
* SD (SDSC), SDHC, SDXC, SDIO, SDUC
* {{Nowrap|{{cvt|32|x|24|x|2.1|mm|frac=64}}}}
* {{Nowrap|{{cvt|32|x|24|x|1.4|mm|frac=64}}}} (as thin as MMC) for '''Thin SD''' (rare)

====<span class="anchor" id="MiniSD"></span>MiniSD====
* miniSD, miniSDHC, miniSDIO
* {{Nowrap|{{cvt|21.5|x|20|x|1.4|mm|frac=64}}}}

====<span class="anchor" id="microSD"></span> microSD====
The micro form factor is the smallest SD card format.<ref name="sdcard_choices">{{cite web|title=About|publisher=SD Association|url=https://www.sdcard.org/consumers/choices/|access-date=2011-05-02}}</ref>
* microSD, microSDHC, microSDXC, microSDUC
* {{Nowrap|{{cvt|15|x|11|x|1|mm|frac=64}}}}

===Transfer modes===

Cards may support various combinations of the following bus types and transfer modes. The SPI bus mode and one-bit SD bus mode are mandatory for all SD families, as explained in the next section. Once the host device and the SD card negotiate a bus interface mode, the usage of the numbered pins is the same for all card sizes.
* '''SPI bus mode:''' Serial Peripheral Interface Bus is primarily used by embedded [[Engineering:Microcontroller|microcontroller]]s. This bus type supports only a 3.3-volt interface. This is the only bus type that does not require a host license.{{Citation needed|date=August 2019}}
* '''One-bit SD bus mode:''' Separate command and data channels and a proprietary transfer format.
* '''Four-bit SD bus mode:''' Uses extra pins plus some reassigned pins. This is the same protocol as the one-bit SD bus mode which uses one command and four data lines for faster data transfer. All SD cards support this mode. UHS-I and UHS-II require this bus type.
* '''Two differential lines SD UHS-II mode:''' Uses two low-voltage differential signalling interfaces to transfer commands and data. UHS-II cards include this interface in addition to the SD bus modes.

The physical interface comprises 9 pins, except that the miniSD card adds two unconnected pins in the center and the microSD card omits one of the two V<sub>SS</sub> (Ground) pins.<ref>{{cite web |url=https://www.sdcard.org/downloads/pls/simplified_specs/part1_410.pdf |title=SD Part 1, Physical Layer Simplified Specification, Version 4.10 |access-date=2014-01-02 |url-status=dead |archive-url=https://web.archive.org/web/20131202232415/https://www.sdcard.org/downloads/pls/simplified_specs/part1_410.pdf |archive-date=2013-12-02 }}</ref>

[[File:MMC-SD-miniSD-microSD-Color-Numbers-Names.gif|thumb|upright|Official pin numbers for each card type (top to bottom): MMC, SD, miniSD, microSD. This shows the evolution from the older MMC, on which SD is based. NOTE: This drawing does not show 8 new UHS-II contacts that were added in spec 4.0.]]

{| class="wikitable" style="text-align:center"
|+ SPI bus mode
|-
! MMC<br/>pin !! SD<br/>pin !! miniSD<br/>pin !! microSD<br/>pin !! Name !! I/O !! Logic !! Description
|-
| 1 ||1 ||1 ||2 ||nCS ||I ||PP ||style="text-align:left"|SPI Card Select [CS] (Negative logic)
|-
| 2 ||2 ||2 ||3 ||DI ||I ||PP ||style="text-align:left"|SPI Serial Data In [MOSI]
|-
| 3 ||3 ||3 ||style="background: gray" | {{sp}} ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| 4 ||4 ||4 ||4 ||VDD ||S ||S ||style="text-align:left"|Power
|-
| 5 ||5 ||5 ||5 ||CLK ||I ||PP ||style="text-align:left"|SPI Serial Clock [SCLK]
|-
| 6 ||6 ||6 ||6 ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| 7 ||7 ||7 ||7 ||DO ||O ||PP ||style="text-align:left"|SPI Serial Data Out [MISO]
|-
| style="background: gray" | {{sp}} ||8 ||8 ||8 ||NC<br/>nIRQ ||.<br/>O ||.<br/>OD ||style="text-align:left"|Unused (memory cards)<br/>Interrupt (SDIO cards) (negative logic)
|-
| style="background: gray" | {{sp}} ||9 ||9 ||1 ||NC ||. ||. ||style="text-align:left"|Unused
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||10 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||11 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|}

{| class="wikitable" style="text-align:center"
|+ One-bit SD bus mode
|-
! MMC<br/>pin !! SD<br/>pin !! miniSD<br/>pin !! microSD<br/>pin !! Name !! I/O !! Logic !! Description
|-
| 1 ||1 ||1 ||2 ||CD ||I/O ||. ||style="text-align:left"|Card detection (by host) and<br/>non-SPI mode detection (by card)
|-
| 2 ||2 ||2 ||3 ||CMD ||I/O ||PP,<br/>OD ||style="text-align:left"|Command,<br/>Response
|-
| 3 ||3 ||3 ||style="background: gray" | {{sp}} ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| 4 ||4 ||4 ||4 ||VDD ||S ||S ||style="text-align:left"|Power
|-
| 5 ||5 ||5 ||5 ||CLK ||I ||PP ||style="text-align:left"|Serial clock
|-
| 6 ||6 ||6 ||6 ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| 7 ||7 ||7 ||7 ||DAT0 ||I/O ||PP ||style="text-align:left"|SD Serial Data 0
|-
| style="background: gray" | {{sp}} ||8 ||8 ||8 ||NC<br/>nIRQ ||.<br/>O ||.<br/>OD ||style="text-align:left"|Unused (memory cards)<br/>Interrupt (SDIO cards) (negative Logic)
|-
| style="background: gray" | {{sp}} ||9 ||9 ||1 ||NC ||. ||. ||style="text-align:left"|Unused
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||10 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||11 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|}

{| class="wikitable" style="text-align:center"
|+ Four-bit SD bus mode
|-
! MMC<br/>pin !! SD<br/>pin !! miniSD<br/>pin !! microSD<br/>pin !! Name !! I/O !! Logic !! Description
|-
| . ||1 ||1 ||2 ||DAT3 ||I/O ||PP ||style="text-align:left"|SD Serial Data 3
|-
| . ||2 ||2 ||3 ||CMD ||I/O ||PP,<br/>OD ||style="text-align:left"|Command,<br/>Response
|-
| . ||3 ||3 ||style="background: gray" | {{sp}} ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| . ||4 ||4 ||4 ||VDD ||S ||S ||style="text-align:left"|Power
|-
| . ||5 ||5 ||5 ||CLK ||I ||PP ||style="text-align:left"|Serial clock
|-
| . ||6 ||6 ||6 ||VSS ||S ||S ||style="text-align:left"|Ground
|-
| . ||7 ||7 ||7 ||DAT0 ||I/O ||PP ||style="text-align:left"|SD Serial Data 0
|-
| style="background: gray" | {{sp}} ||8 ||8 ||8 ||DAT1<br/>nIRQ ||I/O<br/>O ||PP<br/>OD ||style="text-align:left"|SD Serial Data 1 (memory cards)<br/>Interrupt Period (SDIO cards share pin via protocol)
|-
| style="background: gray" | {{sp}} ||9 ||9 ||1 ||DAT2 ||I/O ||PP ||style="text-align:left"|SD Serial Data 2
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||10 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|-
| style="background: gray" | {{sp}} ||style="background: gray" | {{sp}} ||11 ||style="background: gray" | {{sp}} ||NC ||. ||. ||style="text-align:left"|Reserved
|}

Notes:
# Direction is relative to card. I = Input, O = Output.
# PP = [[Engineering:Push–pull output|Push-Pull]] logic, OD = [[Engineering:Open collector|Open-Drain]] logic.
# S = Power Supply, NC = Not Connected (or [[Engineering:Pull-up resistor|logical high]]).

===Interface===
[[File:Sd insides.png|thumb|Inside a 512&nbsp;MB SD card: NAND flash chip that holds the data (bottom) and SD controller (top)]]
[[File:SD-extreMEmory 2GB alt innen.jpg|thumb|upright|Inside a 2&nbsp;GB SD card: two NAND flash chips (top and middle), SD controller chip (bottom)]]
[[File:Pretec 16GB SDHC without cover 20090420.jpg|thumb|upright|Inside a 16&nbsp;GB SDHC card]]

====Command interface====
SD cards and host devices initially communicate through a synchronous one-bit interface, where the host device provides a clock signal that strobes single bits in and out of the SD card. The host device thereby sends 48-bit commands and receives responses. The card can signal that a response will be delayed, but the host device can abort the dialogue.<ref name="SDHCspec"/>

Through issuing various commands, the host device can:<ref name="SDHCspec"/>
* Determine the type, memory capacity and capabilities of the SD card
* Command the card to use a different voltage, different clock speed, or advanced electrical interface
* Prepare the card to receive a block to write to the flash memory, or read and reply with the contents of a specified block.

The command interface is an extension of the MultiMediaCard (MMC) interface. SD cards dropped support for some of the commands in the MMC protocol, but added commands related to copy protection. By using only commands supported by both standards until determining the type of card inserted, a host device can accommodate both SD and MMC cards.

====Electrical interface====
All SD card families initially use a 3.3&nbsp;[[Volt|volt]] electrical interface. On command, SDHC and SDXC cards can switch to 1.8&nbsp;V operation.<ref name="SDHCspec"/>

At initial power-up or card insertion, the host device selects either the Serial Peripheral Interface (SPI) bus or the one-bit SD bus by the voltage level present on Pin 1. Thereafter, the host device may issue a command to switch to the four-bit SD bus interface, if the SD card supports it. For various card types, support for the four-bit SD bus is either optional or mandatory.<ref name="SDHCspec"/>

After determining that the SD card supports it, the host device can also command the SD card to switch to a higher transfer speed. Until determining the card's capabilities, the host device should not use a clock speed faster than 400&nbsp;kHz. SD cards other than SDIO (see below) have a "Default Speed" clock rate of 25&nbsp;MHz. The host device is not required to use the maximum clock speed that the card supports. It may operate at less than the maximum clock speed to conserve power.<ref name="SDHCspec"/> Between commands, the host device can stop the clock entirely.

====MBR and FAT====
Most SD cards ship preformatted with one or more [[Master boot record|MBR partitions]], where the first or only partition contains a [[File system|file system]]. This lets them operate like the hard disk of a [[Engineering:Personal computer|personal computer]]. Per the SD card specification, an SD card is formatted with MBR and the following file system:

* For SDSC cards:
** Capacity of less than 32,680 logical sectors<!-- This is the exact condition as per the SD card spec. For operating systems to properly recognize this as FAT12, the cluster values used on the resulting volume must not be outside the range 002h..FF5h, a condition normally (but not necessarily) met implicitly when applying standard logical geometries on a FAT filesystem with less than 32680 logical sectors. We mention the logical sector count rather than the allowed cluster range here as this article is about SD cards specifically. --> (smaller than 16 MB{{efn|name="here, MB = 1024"|reference=here, MB = 1024<sup>2</sup> B}}): [[FAT12]] with partition type [[Partition type#PID 01h|01h]] and BPB 3.0 or EBPB 4.1<ref name="SDG_2000_SD-P2-V1.0">{{cite book
|title=SD Memory Card Specifications – PART 2 FILE SYSTEM SPECIFICATION – Version 1.0
|author=<!-- Staff writer(s); no by-line -->
|publisher=SD Group, Matsushita Electric Industrial Co., Ltd. (MEI), SanDisk Corporation, Toshiba Corporation
|date=February 2000
|version=1.0}}</ref>
** Capacity of 32,680 to 65,535 logical sectors (between 16&nbsp;MB and 32&nbsp;MB):{{efn|name="here, MB = 1024"}} [[FAT16]] with partition type [[Partition type#PID 04h|04h]] and BPB 3.0 or EBPB 4.1<ref name="SDG_2000_SD-P2-V1.0"/>
** Capacity of at least 65,536 logical sectors (larger than 32&nbsp;MB):{{efn|name="here, MB = 1024"}} [[FAT16B]] with partition type [[Partition type#PID 06h|06h]] and EBPB 4.1<ref name="SDG_2000_SD-P2-V1.0"/>
* For SDHC cards:
** Capacity of less than 16,450,560<!-- CHS: 0..1023 / 0..254 (but not 255!) / 1 (but not 0!)..63 -> limit: 1024x255x63 = 16450560 --> logical sectors (smaller than 7.8&nbsp;GB): [[FAT32]] with partition type [[Partition type#PID 0Bh|0Bh]] and EBPB 7.1
** Capacity of at least 16,450,560 logical sectors (larger than 7.8&nbsp;GB): [[FAT32]] with partition type [[Partition type#PID 0Ch|0Ch]] and EBPB 7.1
* For SDXC cards: [[ExFAT|exFAT]] with partition type [[Partition type#PID 07h|07h]]

Most consumer products that take an SD card expect that it is partitioned and formatted in this way. Universal support for FAT12, FAT16, FAT16B and FAT32 allows the use of SDSC and SDHC cards on most host computers with a compatible SD reader, to present the user with the familiar method of named files in a hierarchical directory tree.{{cn|date=September 2023}}

On such SD cards, standard utility programs such as Mac OS X's "{{Nowrap|[[Software:Disk Utility|Disk Utility]]}}" or Windows' [[Software:SCANDISK|SCANDISK]] can be used to repair a corrupted filing system and sometimes recover deleted files. [[Defragmentation]] tools for FAT file systems may be used on such cards. The resulting consolidation of files may provide a marginal improvement in the time required to read or write the file,<ref name="Fragmentation_and_Speed">{{Citation | url = https://www.sdcard.org/developers/overview/speed_class/ | title = Fragmentation and Speed | publisher = SD Card}}</ref> but not an improvement comparable to defragmentation of hard drives, where storing a file in multiple fragments requires additional physical and relatively slow, movement of a drive head.{{cn|date=September 2023}} Moreover, defragmentation performs writes to the SD card that count against the card's rated lifespan. The write endurance of the physical memory is discussed in the article on flash memory; newer technology to increase the storage capacity of a card provides worse write endurance.{{cn|date=September 2023}}

When reformatting an SD card with a capacity of at least 32&nbsp;MB{{efn|name="here, MB = 1024"}} (65,536 logical sectors or more), but not more than 2&nbsp;GB,{{efn|name="GiB"}} [[FAT16B]] with partition type [[Partition type#PID 06h|06h]] and EBPB 4.1<ref name="SDG_2000_SD-P2-V1.0"/> is recommended if the card is for a consumer device. (FAT16B is also an option for 4&nbsp;GB cards, but it requires the use of 64&nbsp;KB clusters, which are not widely supported.) FAT16B does not support cards above 4&nbsp;GB{{efn|name="GiB"}} at all.

The SDXC specification mandates the use of [[Company:Microsoft|Microsoft]]'s [[Proprietary format|proprietary]] [[ExFAT|exFAT]] file system,<ref name="engadget_sdxc_2t_300m">{{cite web | url = https://www.engadget.com/2009/01/07/sdxc-memory-cards-promise-2tb-of-storage-300mbps-transfer/ |title = SDXC memory cards promise 2 TB of storage, 300 MBps transfer | publisher=Engadget |date= 2009-01-07 |access-date=2010-08-22}}</ref> which sometimes requires appropriate drivers (e.g. <code>exfat-utils</code>/<code>exfat-fuse</code> on Linux).

====Risks of reformatting====
Reformatting an SD card with a different file system, or even with the same one, may make the card slower, or shorten its lifespan. Some cards use [[Wear leveling|wear leveling]], in which frequently modified blocks are mapped to different portions of memory at different times, and some wear-leveling algorithms are designed for the access patterns typical of FAT12, FAT16 or FAT32.<ref>{{cite web|url=https://lwn.net/Articles/428584/ |title=Optimizing Linux with cheap flash drives |publisher=Linux Weekly News|access-date=2011-04-11}}</ref> In addition, the preformatted file system may use a cluster size that matches the erase region of the physical memory on the card; reformatting may change the cluster size and make writes less efficient. The SD Association provides freely downloadable SD Formatter software to overcome these problems for Windows and Mac OS X.<ref name=sdfmt>[https://www.sdcard.org/downloads/formatter/ SD Formatter 3.1 for SD/SDHC/SDXC], SD Association</ref>

SD/SDHC/SDXC memory cards have a "Protected Area" on the card for the SD standard's security function. Neither standard formatters nor the SD Association formatter will erase it. The SD Association suggests that devices or software which use the SD security function may format it.<ref name=sdfmt/>

===Power consumption===
The power consumption of SD cards varies by its speed mode, manufacturer and model.{{cn|date=September 2023}}

During transfer it may be in the range of 66–330&nbsp;mW (20–100&nbsp;mA at a supply voltage of 3.3&nbsp;V). Specifications from TwinMOS Technologies list a maximum of 149&nbsp;mW (45&nbsp;mA) during transfer. Toshiba lists 264–330&nbsp;mW (80–100&nbsp;mA).<ref>{{Citation | url = http://www.toshiba-memory.com/en/micro_sd_cards.html | contribution = microSD & microSDHC Cards | publisher = Toshiba | title = Memory Solutions}}</ref> Standby current is much lower, less than 0.2&nbsp;mA for one 2006 microSD card.<ref>{{Citation | url = http://www.dtt8.com/images/micro-sd%20specification.pdf | publisher = DTT | title = Micro SD specification | url-status = dead | archive-url = https://web.archive.org/web/20130207004550/http://www.dtt8.com/images/micro-sd%20specification.pdf | archive-date = 2013-02-07 }}</ref> If there is data transfer for significant periods, battery life may be reduced noticeably; for reference, the capacity of smartphone batteries is typically around 6&nbsp;Wh (Samsung Galaxy S2: 1650&nbsp;mAh @ 3.7&nbsp;V).

Modern UHS-II cards can consume up to 2.88&nbsp;W, if the host device supports bus speed mode SDR104 or UHS-II. Minimum power consumption in the case of a UHS-II host is 720&nbsp;mW.{{cn|date=September 2023}}

{| class="wikitable" style="text-align:center"
|+ Card requirements in different bus speed modes<ref>{{Citation | url = https://docs.google.com/viewer?url=https://www.sdcard.org/downloads/pls/simplified_specs/part1_410.pdf | contribution = SD Specifications Version 4.10 | publisher = SD Association| title = 3.10.5 – Summary of Bus Speed Mode for UHS-II Card}}</ref>
|-
! Bus speed<br/>mode !! Max. bus<br/>speed<br/>[MB/s] !! Max. clock<br/>frequency<br/>[MHz] !! Signal<br/>voltage<br/>[V] !! SDSC<br/>[W] !! SDHC<br/>[W] !! SDXC<br/>[W]
|-
| HD312 || 312 || 52 || 0.4 || – || 2.88 || 2.88
|-
| FD156 || 156 || 52 || 0.4 || – || 2.88 || 2.88
|-
| SDR104 || 104 || 208 || 1.8 || – || 2.88 || 2.88
|-
| SDR50 || 50 || 100 || 1.8 || – || 1.44 || 1.44
|-
| DDR50 || 50 || 50 || 1.8 || – || 1.44 || 1.44
|-
| SDR25 || 25 || 50 || 1.8 || – || 0.72 || 0.72
|-
| SDR12 || 12.5 || 25 || 1.8 || – || 0.36 || 0.36 / 0.54
|-
| High Speed || 25 || 50 || 3.3 || 0.72 || 0.72 || 0.72
|-
| Default Speed || 12.5 || 25 || 3.3 || 0.33 || 0.36 || 0.36 / 0.54
|}

==Storage capacity and compatibilities==
All SD cards let the host device determine how much information the card can hold, and the specification of each SD family gives the host device a guarantee of the maximum capacity a compliant card reports.

By the time the version 2.0 (SDHC) specification was completed in June 2006,<ref>{{Citation | url = http://www.dramexchange.com/WeeklyResearch/Post/1/492.aspx | title = A look into how SDHC will affect the future Nand Flash market | newspaper = DRAMeXchange | date = December 2006 | access-date = 2007-03-08 | archive-date = 2008-02-04 | archive-url = https://web.archive.org/web/20080204235806/http://www.dramexchange.com/WeeklyResearch/Post/1/492.aspx | url-status = dead }}</ref> vendors had already devised 2&nbsp;GB and 4&nbsp;GB SD cards, either as specified in Version 1.01, or by creatively reading Version 1.00. The resulting cards do not work correctly in some host devices.<ref>{{Citation | url = http://www.hjreggel.net/cardspeed/special-sd.html | contribution = SD Compatibility | title = Card speed – Card Readers and Memory Cards | date = December 1, 2006 | publisher = HJ Reggel}}</ref><ref>{{cite web |url=http://www.eggheadcafe.com/software/aspnet/33338344/winxp-sp3-cant-read-4gb.aspx |title=WinXP SP3 cannot read 4GB SD card in multicard reader |publisher=Egg head cafe |access-date=2010-08-22 |archive-date=2012-07-30 |archive-url=https://archive.today/20120730165858/http://www.eggheadcafe.com/software/aspnet/33338344/winxp-sp3-cant-read-4gb.aspx |url-status=dead }}</ref>

===SDSC cards above 1 GB===
[[File:Sd4gy crop.jpg|thumb|4&nbsp;GB SDSC card]]

SD version 1.00 assumed 512 bytes per block. This permitted SDSC cards up to 4,096 × 512 × 512 B = 1&nbsp;GB.{{efn|name="GiB"}}

Version 1.01 let an SDSC card use a 4-bit field to indicate 1,024 or 2,048 bytes per block instead.<ref name="SDHCspec"/> Doing so enabled cards with 2&nbsp;GB and 4&nbsp;GB capacity, such as the Transcend 4&nbsp;GB SD card, the Memorette 4 GB SD card and the Hoco 4 GB microSD card.{{cn|date=September 2023}}

===Storage capacity calculations===
The format of the Card-Specific Data (CSD) register changed between version 1 (SDSC) and version 2.0 (which defines SDHC and SDXC).

====Version 1====
In version 1 of the SD specification, capacities up to 2&nbsp;GB{{efn|name="GiB"}} are calculated by combining fields of the CSD as follows:

 Capacity = ('''C_SIZE''' + 1) × 2<sup>('''C_SIZE_MULT''' + '''READ_BL_LEN''' + 2)</sup>
 where
  0 ≤ '''C_SIZE''' ≤ 4095,
  0 ≤ '''C_SIZE_MULT''' ≤ 7,
  '''READ_BL_LEN''' is 9 (for 512 bytes/sector) or 10 (for 1024 bytes/sector)

Later versions state (at Section 4.3.2) that a 2&nbsp;GB SDSC card shall set its READ_BL_LEN (and WRITE_BL_LEN) to indicate 1024 bytes, so that the above computation correctly reports the card's capacity, but that, for consistency, the host device shall not request (by CMD16) block lengths over 512 B.<ref name="SDHCspec"/>

====Versions 2 and 3====

In the definition of SDHC cards in version 2.0, the C_SIZE portion of the CSD is 22 bits and it indicates the memory size in multiples of 512&nbsp;KB (the C_SIZE_MULT field is removed and READ_BL_LEN is no longer used to compute capacity). Two bits that were formerly reserved now identify the card family: 0 is SDSC; 1 is SDHC or SDXC; 2 and 3 are reserved.<ref name="SDHCspec"/> Because of these redefinitions, older host devices do not correctly identify SDHC or SDXC cards nor their correct capacity.

* SDHC cards are restricted to reporting a capacity not over 32&nbsp;GB.{{cn|date=September 2023}}
* SDXC cards are allowed to use all 22 bits of the C_SIZE field. An SDHC card that did so (reported C_SIZE > 65,375 to indicate a capacity of over 32&nbsp;GB) would violate the specification. A host device that relied on C_SIZE rather than the specification to determine the card's maximum capacity might support such a card, but the card might fail in other SDHC-compatible host devices.{{cn|date=September 2023}}

Capacity is calculated thus:

 Capacity = ('''C_SIZE''' + 1) × 524288
 where for SDHC 
  4112 ≤ '''C_SIZE''' ≤ 65375 
  ≈2&nbsp;GB ≤ Capacity ≤ ≈32&nbsp;GB
 where for SDXC 
  65535 ≤ '''C_SIZE'''
  ≈32&nbsp;GB ≤ Capacity ≤ 2&nbsp;TB{{cn|date=September 2023}}

Capacities above 4&nbsp;GB can only be achieved by following version 2.0 or later versions. In addition, capacities equal to 4&nbsp;GB must also do so to guarantee compatibility.{{cn|date=September 2023}}

==Openness of specification==
[[File:SD-microSD adaptor.jpg|thumb|upright|Dismantled microSD to SD adapter showing the passive connection from the microSD card slot on the bottom to the SD pins on the top]]

Like most memory card formats, SD is covered by numerous [[Social:Patent|patent]]s and [[Social:Trademark|trademark]]s. Excluding [[Secure Digital#SDIO cards|SDIO]] cards, [[Social:Royalty payment|royalties]] for SD card licenses are imposed for manufacture and sale of memory cards and host adapters (US$1,000/year plus membership at US$1,500/year){{cn|date=September 2023}}

Early versions of the SD specification were available under a [[Social:Non-disclosure agreement|non-disclosure agreement]] (NDA) prohibiting development of [[Open-source software|open-source]] drivers. However, the system was eventually reverse-engineered and free software drivers provided access to SD cards not using DRM. Subsequent to the release of most open-source drivers, the SDA provided a simplified version of the specification under a less restrictive license helping reduce some incompatibility issues.<ref>{{cite web|url=http://www.linux.com/archive/feed/20060 |title=Sharp Linux PDA promotes the use of proprietary SD card, but more open MMC works just fine |date=14 June 2007 |publisher=Linux.com |access-date=2010-08-22}}</ref>

Under a disclaimers agreement, the simplified specification released by the SDA in 2006 – as opposed to that of SD cards – was later extended to the physical layer, ASSD extensions, SDIO and SDIO [[Bluetooth]] Type-A.<ref>[http://www.sdcard.org/developers/tech/sdcard/pls/ Simplified Specification Agreement] {{webarchive|url=https://web.archive.org/web/20081028165644/http://www.sdcard.org/developers/tech/sdcard/pls/ |date=2008-10-28 }} from the SDA's website</ref>

The Simplified Specification<ref>{{cite web|url=https://www.taterli.com/wp-content/uploads/2017/05/Physical-Layer-Simplified-SpecificationV6.0.pdf |title=Simplified Specification}}</ref> is available.

Again, most of the information had already been discovered and [[Software:Linux|Linux]] had a fully free driver for it. Still, building a chip conforming to this specification caused the [[Organization:One Laptop per Child|One Laptop per Child]] project to claim "the first truly Open Source SD implementation, with no need to obtain an SDI license or sign NDAs to create SD drivers or applications."<ref>{{cite web|url=http://mailman.laptop.org/pipermail/community-news/2006-September/000023.html |title=OLPC mailing list archive |publisher=Mailman.laptop.org |access-date=2010-08-22 |archive-url=https://web.archive.org/web/20110412094819/http://mailman.laptop.org/pipermail/community-news/2006-September/000023.html|archive-date=2011-04-12}}</ref>

The proprietary nature of the complete SD specification affects [[Embedded system|embedded system]]s, laptop computers and some desktop computers; many desktop computers do not have card slots, instead using [[Engineering:USB|USB]]-based [[Card reader#Memory card readers|card readers]] if necessary.{{cn|date=September 2023}} These card readers present a standard USB mass storage interface to memory cards, thus separating the operating system from the details of the underlying SD interface.{{cn|date=September 2023}} However, embedded systems (such as portable music players) usually gain direct access to SD cards and thus need complete programming information.{{cn|date=September 2023}} Desktop card readers are themselves embedded systems; their manufacturers have usually paid the SDA for complete access to the SD specifications.{{cn|date=September 2023}} Many notebook computers now include SD card readers not based on USB; device drivers for these essentially gain direct access to the SD card, as do embedded systems.{{cn|date=September 2023}}

The SPI-bus interface mode is the only type that does not require a host license for accessing SD cards.{{cn|date=September 2023}}

[[File:Flash memory cards size.jpg|thumb|upright|Size comparison of various flash cards: SD, [[CompactFlash|CompactFlash]], MMC, [[XD-Picture Card|xD]]]]

==Data recovery==
A malfunctioning SD card can be repaired using specialized equipment, as long as the middle part, containing the flash storage, is not physically damaged. The controller can in this way be circumvented. This might be harder or even impossible in the case of monolithic card, where the controller resides on the same physical die.<ref>{{Cite web|url=https://blog.acelaboratory.com/pc-3000-flash-circuit-board-and-msd-card-preparing-and-soldering.html|title=PC-3000 Flash. How to recover data from a monolith (microSD card)|first=ACELab|last=team}}</ref><ref>{{Cite web|url=https://rusolut.com/monolith-adapters/|title=New adapters for monolithic devices!|date=September 21, 2017}}</ref>

==See also==
* [[Comparison of memory cards]]
* [[Flash memory]]
* [[Microdrive]]
* Serial Peripheral Interface Bus (SPI)
* [[Engineering:Universal Flash Storage|Universal Flash Storage]]

==Footnotes==
{{notelist}}

==References==
{{Reflist}}

==External links==
* [https://www.sdcard.org/ SD Association Official Site]
** [https://www.sdcard.org/downloads/pls/ SD simplified specifications]
** [https://www.sdcard.org/downloads/formatter/ SD Memory Card Formatter]
* [https://web.archive.org/web/20210812130158/http://elm-chan.org/docs/mmc/mmc_e.html How to Use MMC/SDC] elm-chan.org, December 26, 2019
* [https://web.archive.org/web/20210401202138/http://lwn.net/Articles/428584/ Optimizing Linux with cheap flash drives] lwn.net
* [https://web.archive.org/web/20171016194250/https://wiki.linaro.org/WorkingGroups/KernelArchived/Projects/FlashCardSurvey Flash memory card: design, and List of cards and their characteristics] [[Company:Linaro|linaro]]
* [https://havecamerawilltravel.com/fastest-sd-cards/ Independent SD Card Speed Tests]
** [https://havecamerawilltravel.com/sd-cards-explained/ Types of Memory Cards and Sizes]

{{Memory Cards}}

[[Category:Solid-state computer storage media]]

{{Sourceattribution|SD card}}