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[[Image:KeyboardWithPrintScreenRinged.svg|thumb|A 104-key [[Engineering:Personal computer|PC]] {{wipe|United States}} English keyboard layout with System request circled|400x400px]]
{{Short description|Computer key}}
'''System Request''' ('''SysRq''' or '''Sys Req''') is a key on personal computer [[Computer keyboard|keyboards]] that has no standard use. Introduced by [[Company:IBM|IBM]] with the PC/AT, it was intended to be available as a special key to directly invoke low-level [[Operating system|operating system]] functions with no possibility of conflicting with any existing software. A special [[BIOS]] routine – software interrupt 0x15, subfunction 0x85<ref name="intlist">{{cite web|title=Ralf Brown's Interrupt List|url=http://www.delorie.com/djgpp/doc/rbinter/id/30/15.html|access-date=2018-06-21}}</ref> – was added to signal the [[Operating system|OS]] when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the [[Keyboard buffer|keyboard buffer]].
{{Redirect|SysReq|prerequisites for computer software|System requirements}}
[[Image:KeyboardWithPrintScreenRinged.svg|thumb|A 104-key [[Personal computer|PC]] [[United States|US]] [[Social:English language|English]] keyboard layout with System Request circled|400x400px]]
'''System Request''' ('''SysRq''' or '''Sys Req''') is a key on personal computer [[Computer keyboard|keyboards]] that has no standard use. Introduced by [[Company:IBM|IBM]] with the PC/AT, it was intended to be available as a special key to directly invoke low-level [[Operating system|operating system]] functions with no possibility of conflicting with any existing software. A special [[BIOS]] routine – software interrupt 0x15, subfunction 0x85<ref name="intlist">{{cite web|title=Ralf Brown's Interrupt List|url=https://www.delorie.com/djgpp/doc/rbinter/id/30/15.html|access-date=2018-06-21}}</ref> – was added to signal the [[Operating system|OS]] when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the [[Keyboard buffer|keyboard buffer]].


== History ==
== History ==


The specific low level function intended for the SysRq key was to switch between operating systems. When the original IBM-PC was created in 1980, there were three leading competing operating systems: [[Software:PC DOS|PC DOS]], CP/M-86, and UCSD p-System,<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html|title=Original IBM PC Product fact sheet|date=August 12, 1981|publisher=IBM Information Systems Division|access-date=January 13, 2010}}</ref> while [[Software:Xenix|Xenix]] was added in 1983–1984. The SysRq key was added so that multiple operating systems could be run on the same computer, using the capabilities of the [[Engineering:Intel 80286|286]] chip in the PC/AT.<ref>Personal interview with Sandy Meade, creator of the SysRq key</ref>{{vc|date=April 2013}}
The specific low-level function intended for the SysRq key was to switch between operating systems. When the original IBM-PC was created in 1980, there were three leading competing operating systems: [[Software:PC DOS|PC DOS]], CP/M-86, and UCSD p-System,<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html|archive-url=https://web.archive.org/web/20060814072427/http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html|url-status=dead|archive-date=August 14, 2006|title=Original IBM PC Product fact sheet|date=August 12, 1981|publisher=IBM Information Systems Division|access-date=January 13, 2010}}</ref> while [[Software:Xenix|Xenix]] was added in 1983–1984. The SysRq key was added so that multiple operating systems could be run on the same computer, using the capabilities of the [[Engineering:Intel 80286|286]] chip in the PC/AT.<ref>Personal interview with Sandy Meade, creator of the SysRq key</ref>{{vc|date=April 2013}}


A special key was needed because most [[Software|software]] of the day operated at a low level, often bypassing the OS entirely, and typically made use of many hotkey combinations. The use of terminate-and-stay-resident (TSR) programs further complicated matters. To implement a [[Context switch|task switching]] or [[Computer multitasking|multitasking]] environment, it was thought that a special, separate key was needed. This is similar to the way "[[Control-Alt-Delete]]" is used under [[Software:Windows NT|Windows NT]].
A special key was needed because most [[Software|software]] of the day operated at a low level, often bypassing the OS entirely, and typically made use of many hotkey combinations. The use of terminate-and-stay-resident (TSR) programs further complicated matters. To implement a [[Context switch|task switching]] or [[Computer multitasking|multitasking]] environment, it was thought that a special, separate key was needed. This is similar to the way "[[Control-Alt-Delete]]" is used under [[Software:Windows NT|Windows NT]].


On 84-key keyboards (except the 84-key IBM Model M space saver keyboard), SysRq was a key of its own. On the later 101-key keyboard, it shares a physical key with the [[Print screen]] key function. The Alt key must be held down while pressing this dual-function key to invoke SysRq. This continues through modern PC keyboards.<ref name="modern">{{cite web|title=What Are the Sys Rq, Scroll Lock, and Pause Break Keys on My Keyboard?|access-date=March 2, 2020|url=https://www.howtogeek.com/125315/htg-explains-what-are-the-sys-rq-scroll-lock-and-pausebreak-keys-on-my-keyboard/#:~:text=The%20SysRq%20key%20(sometimes%20Sys%20Req)%20is%20an%20abbreviation%20for%20System%20Request.}}</ref>
On 84-key keyboards (except the 84-key IBM Model M space saver keyboard), SysRq was a key of its own. On the later 101-key keyboard, it shares a physical key with the [[Print screen]] key function. The Alt key must be held down while pressing this dual-function key to invoke SysRq. This continues through modern PC keyboards.<ref name="modern">{{cite web|title=What Are the Sys Rq, Scroll Lock, and Pause Break Keys on My Keyboard?|date=26 September 2016 |access-date=March 2, 2020|url=https://www.howtogeek.com/125315/htg-explains-what-are-the-sys-rq-scroll-lock-and-pausebreak-keys-on-my-keyboard/}}</ref>


The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the [[Software:MS-DOS|MS-DOS]] input routines. The keyboard routines in libraries supplied with many high-level languages followed suit. Although it is still included on most PC keyboards manufactured, and though it is used by some{{which|date=July 2019}} debugging software, the key is of no use for the vast majority of users.
The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the [[Software:MS-DOS|MS-DOS]] input routines. The keyboard routines in [[Biology:Library|libraries]] supplied with many high-level languages followed suit. Although it is still included on most PC keyboards manufactured, and though it is used by some{{which|date=July 2019}} debugging software, the key is of no use for the vast majority of users.


On the Hyundai/Hynix Super-16 computer, pressing {{key press|Ctrl|SysRq}} will hard boot the system (it will reboot when {{key press|Ctrl|Alt|Del}} is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).{{Fact|date=January 2008}}
On the Hyundai/Hynix Super-16 computer, pressing {{key press|Ctrl|SysRq}} will hard boot the system (it will reboot when {{key press|Ctrl|Alt|Del}} is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).{{Fact|date=January 2008}}
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In [[Software:Linux|Linux]], the [[Software:Kernel (operating system)|kernel]] can be configured to provide functions for system [[Debugging|debugging]] and crash recovery.<ref name="linux">{{cite web|title=Linux Magic System Request Key Hacks|work=Linux kernel|url=https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html|access-date=2018-06-21}}</ref>  This use is known as the "[[Magic SysRq key|magic SysRq key]]".
In [[Software:Linux|Linux]], the [[Software:Kernel (operating system)|kernel]] can be configured to provide functions for system [[Debugging|debugging]] and crash recovery.<ref name="linux">{{cite web|title=Linux Magic System Request Key Hacks|work=Linux kernel|url=https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html|access-date=2018-06-21}}</ref>  This use is known as the "[[Magic SysRq key|magic SysRq key]]".


[[Company:Microsoft|Microsoft]] has also used SysRq for various [[Operating system|OS]]- and application-level [[Debugger|debugger]]s. In the [[Software:CodeView|CodeView debugger]], it was sometimes used to break into the debugging during program execution.<ref name="mskb43648">{{cite web|title=Returning Control to CodeView|work=Microsoft Knowledge Base|url=http://support.microsoft.com/kb/43648|access-date=January 8, 2008|archiveurl=https://web.archive.org/web/20081108021540/http://support.microsoft.com/kb/43648|archivedate=November 8, 2008|url-status=dead}}</ref> For the [[Software:Windows NT|Windows NT]] remote kernel debugger, it can be used to force the system into the debugger.<ref name="mskb900093">{{cite web|title=How to enable a remote kernel debugger connection on a computer that is running Windows Server 2003 with Service Pack 1|work=Microsoft Knowledge Base|url=http://support.microsoft.com/kb/900093|access-date=January 8, 2008|archiveurl=https://web.archive.org/web/20121021034022/http://support.microsoft.com/kb/900093|archivedate=October 21, 2012|url-status=dead}}</ref>
[[Company:Microsoft|Microsoft]] has also used SysRq for various [[Operating system|OS]]- and [[Application software|application]]-level [[Debugger|debugger]]s. In the [[Software:CodeView|CodeView debugger]], it was sometimes used to break into the debugging during program execution.<ref name="mskb43648">{{cite web|title=Returning Control to CodeView|work=Microsoft Knowledge Base|url=http://support.microsoft.com/kb/43648|access-date=January 8, 2008|archiveurl=https://web.archive.org/web/20081108021540/http://support.microsoft.com/kb/43648|archivedate=November 8, 2008|url-status=dead}}</ref> For the [[Software:Windows NT|Windows NT]] remote kernel debugger, it can be used to force the system into the debugger.<ref name="mskb900093">{{cite web|title=How to enable a remote kernel debugger connection on a computer that is running Windows Server 2003 with Service Pack 1|work=Microsoft Knowledge Base|url=http://support.microsoft.com/kb/900093|access-date=January 8, 2008|archiveurl=https://web.archive.org/web/20121021034022/http://support.microsoft.com/kb/900093|archivedate=October 21, 2012|url-status=dead}}</ref>


On modern Windows "Alt + [[Print screen]]" (which is the shortcut for SysRq on most modern keyboards <ref name="modern" />) copies an image of the current active window, instead of the entire screen as Print Screen alone would.<ref>{{cite web|title=Copy the window or screen contents|access-date=March 2, 2020|url=https://support.microsoft.com/en-us/office/copy-the-window-or-screen-contents-98c41969-51e5-45e1-be36-fb9381b32bb7#:~:text=Copy%20only%20the%20image%20of%20the%20active%20window}}</ref>
On modern Windows and some Linux desktop environments "Alt + [[Print screen]]" (which is the shortcut for SysRq on most modern keyboards<ref name="modern" />) copies an image of the current active window, instead of the entire screen as Print Screen alone would.<ref>{{cite web|title=Copy the window or screen contents|access-date=March 2, 2020|url=https://support.microsoft.com/en-us/office/copy-the-window-or-screen-contents-98c41969-51e5-45e1-be36-fb9381b32bb7}}</ref>


== Similar keys ==
== Similar keys ==
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==External links==
==External links==


{{Keyboard}}
{{keyboard keys}}


{{DEFAULTSORT:System Request}}
{{DEFAULTSORT:System Request}}

Latest revision as of 15:21, 16 May 2026

Short description: Computer key
"SysReq" redirects here. For prerequisites for computer software, see System requirements.
A 104-key PC US English keyboard layout with System Request circled

System Request (SysRq or Sys Req) is a key on personal computer keyboards that has no standard use. Introduced by IBM with the PC/AT, it was intended to be available as a special key to directly invoke low-level operating system functions with no possibility of conflicting with any existing software. A special BIOS routine – software interrupt 0x15, subfunction 0x85[1] – was added to signal the OS when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the keyboard buffer.

History

The specific low-level function intended for the SysRq key was to switch between operating systems. When the original IBM-PC was created in 1980, there were three leading competing operating systems: PC DOS, CP/M-86, and UCSD p-System,[2] while Xenix was added in 1983–1984. The SysRq key was added so that multiple operating systems could be run on the same computer, using the capabilities of the 286 chip in the PC/AT.[3][unreliable source?]

A special key was needed because most software of the day operated at a low level, often bypassing the OS entirely, and typically made use of many hotkey combinations. The use of terminate-and-stay-resident (TSR) programs further complicated matters. To implement a task switching or multitasking environment, it was thought that a special, separate key was needed. This is similar to the way "Control-Alt-Delete" is used under Windows NT.

On 84-key keyboards (except the 84-key IBM Model M space saver keyboard), SysRq was a key of its own. On the later 101-key keyboard, it shares a physical key with the Print screen key function. The Alt key must be held down while pressing this dual-function key to invoke SysRq. This continues through modern PC keyboards.[4]

The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the MS-DOS input routines. The keyboard routines in libraries supplied with many high-level languages followed suit. Although it is still included on most PC keyboards manufactured, and though it is used by some[which?] debugging software, the key is of no use for the vast majority of users.

On the Hyundai/Hynix Super-16 computer, pressing will hard boot the system (it will reboot when is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).[citation needed]

Modern uses

In Linux, the kernel can be configured to provide functions for system debugging and crash recovery.[5] This use is known as the "magic SysRq key".

Microsoft has also used SysRq for various OS- and application-level debuggers. In the CodeView debugger, it was sometimes used to break into the debugging during program execution.[6] For the Windows NT remote kernel debugger, it can be used to force the system into the debugger.[7]

On modern Windows and some Linux desktop environments "Alt + Print screen" (which is the shortcut for SysRq on most modern keyboards[4]) copies an image of the current active window, instead of the entire screen as Print Screen alone would.[8]

Similar keys

IBM 3270-type console keyboards of the IBM System/370 mainframe computer, created in 1970, had an operator interrupt key that was used to cause the operating system such as VM/370 or MVS to allow the console to give input to the operating system.

See also

References

  1. ↑ "Ralf Brown's Interrupt List". https://www.delorie.com/djgpp/doc/rbinter/id/30/15.html. 
  2. ↑ "Original IBM PC Product fact sheet". IBM Information Systems Division. August 12, 1981. http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html. 
  3. ↑ Personal interview with Sandy Meade, creator of the SysRq key
  4. ↑ 4.0 4.1 "What Are the Sys Rq, Scroll Lock, and Pause Break Keys on My Keyboard?". 26 September 2016. https://www.howtogeek.com/125315/htg-explains-what-are-the-sys-rq-scroll-lock-and-pausebreak-keys-on-my-keyboard/. 
  5. ↑ "Linux Magic System Request Key Hacks". Linux kernel. https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html. 
  6. ↑ "Returning Control to CodeView". Microsoft Knowledge Base. Archived from the original on November 8, 2008. https://web.archive.org/web/20081108021540/http://support.microsoft.com/kb/43648. 
  7. ↑ "How to enable a remote kernel debugger connection on a computer that is running Windows Server 2003 with Service Pack 1". Microsoft Knowledge Base. Archived from the original on October 21, 2012. https://web.archive.org/web/20121021034022/http://support.microsoft.com/kb/900093. 
  8. ↑ "Copy the window or screen contents". https://support.microsoft.com/en-us/office/copy-the-window-or-screen-contents-98c41969-51e5-45e1-be36-fb9381b32bb7. 
IBM PC keyboard (Windows, US layout)v · d · e
Esc F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 PrtScn/
SysRq 		Scroll
Lock 		Pause/
Break
TildeExclamation markAt signNumber signDollar signPercent signCaretAmpersandAsteriskParenthesisParenthesisUnderscorePlus signBackspaceGrave accent1 (number)2 (number)3 (number)4 (number)5 (number)6 (number)7 (number)8 (number)9 (number)0 (number)Hyphen-minusEquals signBackspaceTab keyQWERTYUIOPCurly bracketCurly bracketVertical barTab keyqWERTYUIOPSquare bracketSquare bracketBackslashCaps lockASDFGHJKLColon (punctuation)Quotation markEnter keyCaps lockASDFGhJKLSemicolonApostropheEnter keyShift keyZXCVBNMBracketBracketQuestion markShift keyShift keyZXCVBNMComma (punctuation)Full stopSlash (punctuation)Shift keyControl keyWindows keyAlt keySpace barAlt keyWindows keyMenu keyControl key
 Insert Home PgUp Num
Lock 		∕ ∗ −
Delete End PgDn 7 8 9 +
4 5 6
↑ 1 2 3 Enter
← ↓ →    0
   Ins 		 . 
Del



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