View source for 1-bit computing

{{Short description|Computer architecture bit width}}
{{Use list-defined references|date=June 2022}}
{{Computer architecture bit widths}}
[[File:MC14500BCP.jpg|thumb|1-bit [[Programmable logic controller|programmable logic controller]] MC14500BCP]]

In [[Computer architecture|computer architecture]], '''1-bit''' [[Integer (computer science)|integer]]s or other [[Data (computing)|data]] units are those that are {{nowrap|1 [[Bit|bit]]}} (1/8 [[Octet (computing)|octet]]) wide. Also, 1-bit [[Central processing unit|central processing unit]] (CPU) and [[Arithmetic logic unit|arithmetic logic unit]] (ALU) architectures are those that are based on [[Processor register|register]]s of that size.

There are no computers or [[Engineering:Microcontroller|microcontroller]]s of any kind that are exclusively 1-bit for all registers and [[Engineering:Address bus|address bus]]es. A 1-bit register can only store 2<sup>1</sup> different values, i.e. 0 or 1 (off or on, respectively). This is very restrictive and therefore not enough for a [[Program counter|program counter]] which, on modern systems, is implemented in an on-chip register, but is not implemented on-chip in some 1-bit systems. [[Opcode]]s for at least one 1-bit processor architecture were 4-bit and the address bus was 8-bit.

While 1-bit computing is mostly obsolete, 1-bit [[Serial communication|serial communication]] is still used in modern computers, that are otherwise e.g. 64-bit, and thus also have much larger buses.

While 1-bit CPUs are obsolete, the first [[Chemistry:Carbon nanotube computer|carbon nanotube computer]] from 2013 is a 1-bit [[One-instruction set computer|one-instruction set computer]] (and has only 178 transistors; since it has only one instruction<!-- SUBNEG (subtract and branch if negative) --> though it can emulate 20 [[MIPS architecture|MIPS]] instructions).<ref name="Courtland_2013"/>

== 1-bit ==
A [[Serial computer|serial computer]] processes data a single bit at a time. For example, the [[Engineering:PDP-8|PDP-8/S]] was a [[12-bit|12-bit]] computer using a 1-bit ALU, processing the 12 bits serially.<ref name="DEC_1969"/>

An example of a 1-bit computer built from discrete logic SSI chips is the Wang 500<!-- Wang 500-0, Wang 520 --> (1970/1971) calculator<ref name="Koblentz_2004"/><ref name="Wang_1974_Schematics"/> as well as the Wang 1200<!-- including Wang 1220 and 1222. The 1222, however, also had an Intel 4004 --> (1971/1972)<ref name="Battle_2010"/> word processor series developed by [[Organization:Wang Laboratories|Wang Laboratories]].

An example of a 1-bit architecture that was marketed as a CPU is the [[Engineering:Motorola MC14500B|Motorola MC14500B]] Industrial Control Unit (ICU),<ref name="Motorola_1977_MC14500B"/><ref name="Motorola_1995_MC14500B"/> introduced in 1977 and manufactured at least up into the mid 1990s.<ref name="Motorola_1995_MC14500B"/> Its manual states:

{{quote|[…] Computers and microcomputers may also be used, but they tend to overcomplicate the task and often require highly trained personnel to develop and maintain the system. A simpler device, designed to operate on inputs and outputs one-at-a-time and configured to resemble a relay system, was introduced. These devices became known to the controls industry as [[Programmable logic controller|programmable logic controller]]s (PLC). The Motorola MC14500B Industrial Control Unit (ICU) is the monolithic embodiment of the PLC's central architecture […]

There are functions for which one bit machines are poorly suited. […] Under some circumstances, a combination of an MC6800 MPU and an MC14500B ICU may be the best solution. […]

''Program Counter''<br>
The [[Program counter|program counter]] is composed of two MC145168 binary up-[[Counter (digital)|counters]] chained together to create 8 bits of memory address. This gives the system the capability of addressing 256 separate memory words. The counters are configured to count up on the rising edge of the ICU clock (CLK) signal and reset to zero when the ICU is reset. Notice that the program counter count sequence cannot be altered by any operation of the ICU. This confirms that the system is configured to have a looping control structure.

''Memory''<br>
The memory for this system is composed of one MCM7641<!-- MCM764l with "L" assumed typo/OCR error --> 512-word by 8 bit PROM memory. Because the program counter is only 8 bits wide, only 256 words, (half of the memory), can be used at any one time. However, by wiring the most significant bit of the memory's address high or low, the system designer can select between two separate programs with only a jumper option. This might be a desirable feature if extremely fast system changes are required.|source=MC14500B Industrial Control Unit Handbook<ref name="Motorola_1977_MC14500B"/>}}

One of the computers known to be based on this CPU was the WDR 1-bit computer.<ref name="Ludwig_1986_WDR-1"/> A typical sequence of instructions from a program for a 1-bit architecture might be:

* load digital input 1 into a 1-bit register;
* [[Logical disjunction|OR]] the value in the 1-bit register with input 2, leaving the result in the register;
* write the value in the 1-bit register to output 1.

This architecture was considered superior for programs making decisions rather than performing arithmetic computations, for [[Ladder logic|ladder logic]] as well as for serial data processing.<ref name="Motorola_1977_MC14500B"/>

There are also several design studies for 1-bit architectures in academia, and corresponding 1-bit logic can also be found in programming.

Other examples of 1-bit architectures are [[Programmable logic controller|programmable logic controller]]s (PLCs), programmed in [[Instruction list|instruction list]] (IL).

Several early [[Massively parallel|massively parallel]] computers used 1-bit architectures for the processors as well. Examples include the May 1983 [[Engineering:Goodyear MPP|Goodyear MPP]] and the 1985 [[Connection Machine]]. By using a 1-bit architecture for the individual processors a very large array (e.g. the Connection Machine had 65,536 processors) could be constructed with the chip technology available at the time. In this case the slow computation of a 1-bit processor was traded off against the large number of processors.

1-bit CPUs can now be considered obsolete; not many kinds have ever been produced, still {{as of|2022|lc=y}} some MC14500B chips are available from brokers for obsolete parts.<ref name="Digipart_2022"/><ref name="eBay_2022"/>

== See also ==
* [[Bit-serial architecture]]
* [[Bit banging]]
* [[Bit slicing]]
* [[Turing machine]]
* Enhanced Serial Peripheral Interface (eSPI) allows 1-bit communication

== References ==
{{reflist|refs=
<ref name="Courtland_2013">{{cite web |title=First Computer Made From Carbon Nanotubes Debuts - The modest 1-bit, 1 kHz machine could usher in a new post-silicon era |author-first=Rachel |author-last=Courtland |date=2013-09-25 |website=IEEE Spectrum: Technology, Engineering, and Science News |url=https://spectrum.ieee.org/tech-talk/semiconductors/devices/first-computer-made-from-carbon-nanotubes-debuts |access-date=2021-04-18 |url-status=live |archive-url=https://web.archive.org/web/20220615190932/https://spectrum.ieee.org/first-computer-made-from-carbon-nanotubes-debuts |archive-date=2022-06-15}}</ref>
<ref name="DEC_1969">{{cite book |title=PDP-8/S Maintenance Manual |chapter=III. System Logic - 3.4. Control Circuits - 3.4.1 Adder |date=August 1969 |orig-date=October 1967 |edition=4th printing |publisher=[[Company:Digital Equipment Corporation|Digital Equipment Corporation]] |location=Maynard, Massachusetts, US |id=F-87S |pages=3-14–3-15 |url=http://www.bitsavers.org/pdf/dec/pdp8/pdp8s/PDP8S_MaintMan.pdf |access-date=2022-06-15 |url-status=live |archive-url=https://web.archive.org/web/20211023025507/http://www.bitsavers.org/pdf/dec/pdp8/pdp8s/PDP8S_MaintMan.pdf |archive-date=2021-10-23}} (191 pages)</ref>
<ref name="Koblentz_2004">{{cite interview |title=LED calculators rule her house |interviewer-first=Evan |interviewer-last=Koblentz |author-first=Katie<!-- aka Kathie / Katherine / Ken --> |author-last=Wasserman |journal=Computer Collector Newsletter / Technology Rewind |orig-date=January 2004 |date=March 2006 |url=http://www.snarc.net/tr/katie-led.htm |access-date=2017-05-20 |url-status=live |archive-url=https://archive.today/20191227180243/http://www.snarc.net/tr/katie-led.htm |archive-date=2019-12-27 |quote=Probably my most favorite is the Wang 500. It's got several unique things about it: a very unusual ROM memory made of hundreds of long enamel-coated wires wrapped around iron cores; a super-fast single-bit CPU built out of SSI logic chips; and of course tons of really cool-looking colorful keys.}}</ref>
<ref name="Wang_1974_Schematics">{{cite book |title=Product Service - Schematic manual |publisher=Wang Laboratories, Inc. |date=1974 |id=03-0019-0 |url=http://www.thebattles.net/oddments/wang/Wang_500_schematics.pdf |access-date=2017-05-20 |url-status=live |archive-url=https://web.archive.org/web/20170520161939/http://www.thebattles.net/oddments/wang/Wang_500_schematics.pdf |archive-date=2017-05-20}}</ref>
<ref name="Battle_2010">{{cite web |title=Wang 1200 - Wang WP History |author-first=Jim |author-last=Battle |date=2010-03-07 |url=http://www.wang1200.org/history.html |access-date=2017-05-21 |url-status=live |archive-url=https://web.archive.org/web/20170521004512/http://www.wang1200.org/history.html |archive-date=2017-05-21}}</ref>
<ref name="Motorola_1977_MC14500B">{{cite book |title=Motorola MC14500B Industrial Control Unit Handbook - Theory and Operation of a CMOS one-bit processor compatible with B series CMOS devices |author-first1=Vern |author-last1=Gregory |author-first2=Brian |author-last2=Dellande |author-first3=Ray |author-last3=DiSilvestro |author-first4=Terry |author-last4=Malarkey |author-first5=Phil |author-last5=Smith |author-first6=Mike |author-last6=Hadley |publisher=Motorola Semiconductor Products Inc. |date=1977 |id=33-B78/8.0 |url=http://tinymicros.com/mediawiki/images/e/ec/MC14500B_Handbook.pdf |access-date=2017-05-20 |url-status=live |archive-url=https://web.archive.org/web/20220401141059/https://tinymicros.com/mediawiki/images/e/ec/MC14500B_Handbook.pdf |archive-date=2022-04-01}} (NB. Also available in German language under the title "Motorola MC14500B Industrial Control Unit Handbuch - Theorie und Anwendung eines Ein-Bit-CMOS-Prozessors".)</ref>
<ref name="Motorola_1995_MC14500B">{{cite book |chapter=Industrial Control Unit MC14500B |series=Semiconductor Technical Data |title=Motorola CMOS Logic Data |publisher=[[Company:Motorola|Motorola]] |edition=revision 3 |date=1995<!-- |orig-date=1/94? --> |pages=306–313 |url=http://www.brouhaha.com/~eric/retrocomputing/motorola/mc14500b/mc14500brev3.pdf |access-date=2012-08-01 |url-status=live |archive-url=https://web.archive.org/web/20170520123638/http://www.brouhaha.com/~eric/retrocomputing/motorola/mc14500b/mc14500brev3.pdf |archive-date=2017-05-20}}</ref>
<ref name="Ludwig_1986_WDR-1">{{cite book |title=Fast alles über den WDR-1-Bit-Computer |language=de |author-first1=Volker |author-last1=Ludwig |author-first2=Klaus |author-last2=Paschenda |author-first3=Heinz |author-last3=Schepers |author-first4=Hermann-Josef |author-last4=Terglane |author-first5=Klaus |author-last5=Grannemann |author-first6=Burkhard |author-last6=John |author-first7=Hermann |author-last7=Komar |author-first8=Ludwig |author-last8=Meinersen |publisher=DATANorf |location=Neuss & Recklinghausen, Germany |date=1986 |url=http://wdr-1-bit-computer.talentraspel.de/documents/wdr_1-40.pdf |access-date=2017-05-20 |url-status=live |archive-url=https://web.archive.org/web/20170520131325/http://wdr-1-bit-computer.talentraspel.de/documents/wdr_1-40.pdf |archive-date=2017-05-20}}</ref>
<ref name="Digipart_2022">{{cite web |title=MC14500B Price & Stock |website=www.digipart.com |url=https://www.digipart.com/part/mc14500b?gclid=EAIaIQobChMIy8i09b7R5QIVT0HTCh1YgQZzEAEYAiAAEgJza_D_BwE |access-date=2021-03-29 |url-status=live |archive-url=https://web.archive.org/web/20220615184147/https://www.digipart.com/part/mc14500b |archive-date=2022-06-15}}</ref>
<ref name="eBay_2022">{{cite web |title=MC14500B |website=www.ebay.com |url=https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=MC14500B&_sacat=0 |access-date=2019-11-04 |url-status=live |archive-url=https://web.archive.org/web/20220615184524/https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=MC14500B&_sacat=0 |archive-date=2022-06-15}}</ref>
}}

== Further reading ==
* {{cite web |title=The famous/infamous MC14500 |author-first=Dieter |author-last=Mueller |date=2005 |orig-date=2004 |url=http://www.6502.org/users/dieter/m14500/m14500.htm |access-date=2018-07-18 |url-status=live |archive-url=https://web.archive.org/web/20170803122314/http://www.6502.org/users/dieter/m14500/m14500.htm |archive-date=2017-08-03}}
* {{cite web |title=MC14500 and arithmetic |author-first=Dieter |author-last=Mueller |date=2008 |url=http://www.6502.org/users/dieter/a3/a3_5.htm |access-date=2018-07-18 |url-status=live |archive-url=https://web.archive.org/web/20170520222644/http://www.6502.org/users/dieter/a3/a3_5.htm |archive-date=2017-05-20}}
* {{cite web |title=A MC14500 modification |author-first=Dieter |author-last=Mueller |date=2008 |url=http://www.6502.org:80/users/dieter/a3/a3_6.htm |access-date=2018-07-18 |url-status=live |archive-url=https://web.archive.org/web/20170320114921/http://www.6502.org/users/dieter/a3/a3_6.htm |archive-date=2017-03-20 |ref=none}}

== External links ==
* {{cite web |title=WDR-1-Bit Computer |author-first1=Thierry |author-last1=Schembri |author-first2=Sylvain |author-last2=Bizoirre |author-first3=Olivier |author-last3=Boisseau |author-first4=Pierre-Emmanuel |author-last4=Chauvaud |work=OLD-COMPUTERS.COM |url=https://www.old-computers.com/museum/computer.asp?st=1&c=834 |access-date=2017-05-20 |url-status=live |archive-url=https://web.archive.org/web/20170520141901/http://www.old-computers.com/museum/computer.asp?st=1&c=834 |archive-date=2017-05-20}}

{{CPU technologies}}

[[Category:Data unit]]
[[Category:Programmable logic controllers]]

{{Sourceattribution|1-bit computing}}