Editing 4-bit computing

{{Short description|Computer architecture bit width}}
{{Use dmy dates|date=February 2020|cs1-dates=y}}
{{Computer architecture bit widths}}

'''4-bit computing''' is the use of [[computer architecture]]s in which [[integer (computer science)|integers]] and other [[data (computer science)|data]] units are 4 [[bit]]s wide. 4-bit [[central processing unit]] (CPU) and [[arithmetic logic unit]] (ALU) architectures are those that are based on [[processor register|registers]] or [[bus (computing)|data buses]] of that size. A group of four bits is also called a [[nibble]] and has 2<sup>4</sup> = 16 possible values, with a range of 0 to 15.

4-bit computation is obsolete, i.e. CPUs supporting 4-bit as the maximum size. However, 4-bit integers (or smaller), and 4-bit floating point is gaining ground for AI, large-language models.<ref>{{cite conference |arxiv=2310.16836 |doi=10.18653/v1/2023.emnlp-main.39 |title=LLM-FP4: 4-Bit Floating-Point Quantized Transformers |book-title=Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing |date=2023 |last1=Liu |first1=Shih-Yang |last2=Liu |first2=Zechun |last3=Huang |first3=Xijie |last4=Dong |first4=Pingcheng |last5=Cheng |first5=Kwang-Ting |pages=592–605 }}</ref>

4-bit processors were widely used in [[electronic calculator]]s and other roles where decimal math was used, like electronic [[cash register]]s, [[microwave oven]] timers, and so forth. This is because a 4-bit value holds a single [[binary-coded decimal]] (BCD) digit, making it a natural size for directly processing decimal values. As a 4-bit value is generally too small to hold a [[memory address]] for real-world programs or data, the [[address bus]] of these systems was generally larger. For instance, the canonical 4-bit [[microprocessor]], the [[Intel 4004]], had a 12-bit address format.

4-bit designs were used only for a short period when [[integrated circuit]]s were still expensive, and were found primarily in cost-sensitive roles. While 4-bit computing is mostly obsolete, 4-bit values are still used in the same decimal-centric roles they were developed for, and modern implementations are generally much wider and process multiple 4-bit values in parallel. An example of such a system is the [[HP Saturn]] design of the 1980s. By the 1990s, most such uses had been replaced by general purpose binary designs.

== History ==
[[File:Alps remote control BHR970001B - NEC D63GS-7525.jpg|thumb|20-pin PSOP – NEC D63GS: a 4-bit microcontroller for [[infrared remote control]] transmission]]
[[File:Intel C4004 greytraces CPU.jpg|thumb|left|16-pin DIP – Intel C4004]]
[[File:Olympia CD700 Desktop Calculator. 1971.Microprogrammable Arithmetic Processor System Devices (MAPS).jpg|thumb|Olympia CD700 Desktop Calculator using the National Semiconductor MAPS MM570X [[bit-serial]] 4-bit microcontroller]]
[[File:Alps remote control BHR970001B-7517.jpg|thumb|left|Infrared remote control PCB – an [[infrared remote control]] transmitter controlled by a NEC D63GS 4-bit microcontroller]]

A 4-bit processor may seem limited, but it is a good match for calculators, where each decimal digit fits into four bits.<ref name="Shirriff_TMS1000" />

Some of the first [[microprocessor]]s had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the [[binary-coded decimal]] (BCD-based) [[Intel 4004]],<ref name="Mack_2005" /><ref name="Hofstra_History" /> developed for calculator applications in 1971; it had a 4-bit word length, but had 8-bit instructions and 12-bit addresses. It was succeeded by the [[Intel 4040]], which added [[interrupt]] support and a variety of other new features.

The first commercial single-chip computer was the 4-bit [[Texas Instruments]] [[TMS 1000]] (1974).<ref name="Shirriff_TMS1000">{{cite web |author=Ken Shirriff |url=https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html |title=Reverse engineering RAM storage in early Texas Instruments calculator chips}}</ref> It contained a 4-bit [[central processing unit|CPU]] with a [[Harvard architecture]] and 8-bit-wide instructions, an on-chip instruction ROM, and an on-chip data RAM with 4-bit words.<ref name="TI_1976_TMS1000" />

The [[Rockwell PPS-4]] was another early 4-bit processor, introduced in 1972, which had a long lifetime in handheld games and similar roles. It was steadily improved and by 1975 been combined with several support chips to make a one-chip computer.<ref>{{cite web |url=http://www.antiquetech.com/?page_id=796 |title=Rockwell PPS-4}}</ref>

The 4-bit processors were programmed in [[assembly language]] or [[Forth (programming language)|Forth]], e.g. "MARC4 Family of 4 bit Forth CPU"<ref name="UT_Forth" /> (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for [[microcontroller]]s, 8-bit and larger), such as the [[C (programming language)|C programming language]], do not support 4-bit data types (C, and [[C++]], and more languages require that the size of the [[character (computing)#char|<code>char</code>]] data type be at least 8 bits,<ref name="ISOIEC9899_1999_1" /> and that all data types other than bitfields have a size that is a multiple of the character size<ref name="ISOIEC9899_1999_2" /><ref name="Cline" /><ref name="CPP" />).

The 1970s saw the emergence of 4-bit software applications for mass markets like pocket calculators. During the 1980s, 4-bit microprocessors were used in [[handheld electronic game]]s to keep costs low.

In the 1970s and 1980s, a number of research and commercial computers used [[bit slicing]], in which the CPU's [[arithmetic logic unit]] (ALU) was built from multiple 4-bit-wide sections, each section including a chip such as an [[AMD Am2900|Am2901]] or [[74181]].

The [[Zilog Z80]] (discontinued in 2024), although it is an 8-bit microprocessor, has a 4-bit ALU.<ref name="Shima_Z80" /><ref name="Shirriff_Z80" />

Although the [[Data General Nova]] is a series of 16-bit minicomputers, the original Nova and the Nova 1200 internally processed numbers 4 bits at a time with a 4-bit ALU,<ref>{{ cite interview | first = Gardner | last = Hendrie | title = Oral History of Edson (Ed) D. de Castro | date = 22 November 2002 | url = http://archive.computerhistory.org/resources/access/text/2012/07/102702207-05-01-acc.pdf | pages = 44 }}</ref> sometimes called "nybble-serial".<ref>[https://rcsri.org/collection/nova-1200/ "Nova 1200"]</ref>

The [[HP Saturn]] processors, used in many [[Hewlett-Packard]] calculators between 1984<!-- intro of HP-71B --> and 2003<!-- when the HP49 was discontinued and replaced by an ARM based model developed by Kinpo --> <!-- EOL announcement of HP 50g --> (including the [[HP&nbsp;48 series]] of scientific calculators) are "4-bit" (or hybrid 64-/4-bit) machines; as the Intel 4004 did, they string multiple 4-bit words together, e.g. to form a 20-bit memory address, and most of the registers are 64 bits wide, storing 16 4-bit digits.<!-- Its instructions were 10 bits wide.--><!-- The previous statement is factually inaccurate and not supported by the cited sources --><!-- <ref name="HPM">{{cite web |url=http://www.hpmuseum.org/techcpu.htm |title=HP CPU and Programming |access-date=2014-01-14}}</ref> --><!-- This reference is invalid because it points to a page which describes the microarchitectures of the HP41 and older calculators which did not use the Saturn. The reference has been updated to point to the H.P. Saturn specific page. --><ref name="HPM_Saturn" /><ref name="Grack_Saturn" /><ref name="HPCalc_Saturn" /><!--{{Off-topic|date=December 2015|HP Saturn}}Since 2003, new Saturn-based HP calculators{{Dubious |date=December 2015| reason=These are not "Saturn-based" processors. The "Saturn+" isn't even a Saturn processor, but an emulation of one.}} (including the [[HP 49/50 series]]) use a 32-bit processor with an [[ARM920T]] core to emulate an extended Saturn processor architecture named [[HP Saturn+|Saturn+]] at a higher speed. -->

In addition, some early calculators{{snd}} such as the 1967 [[Casio AL-1000]], the 1972 [[Sinclair Executive]], and the aforementioned 1984 [[HP Saturn]]{{snd}} had 4-bit [[datapath]]s that accessed their registers 4 bits (one BCD digit) at a time.<ref>[http://www.vintagecalculators.com/html/casio_al-1000.html "Desk Electronic Calculators: Casio AL-1000"]</ref>

== Uses ==
[[File:National_Semiconductor_COP410L_NGS_top_metal.jpg|thumb|National Semiconductor COP410L, a low-end 4-bit microcontroller. 512 bytes of ROM in upper left corner, 128 bits of RAM in upper right corner. Click to zoom.]]
One bicycle computer specifies that it uses a "4 bit, 1-chip microcomputer".<ref name="Cateye" /> Other typical uses include [[coffeemaker|coffee makers]], [[remote control|infrared remote controls]],<ref name="RenesasPD67" /> and [[security alarm]]s.<ref name="Haskell_MC" /><!-- "4-bit" or "4 bit" isn't actually in the source, 8-bit PIC is, and "Includes coffee makers, burglar alarms, TV remote controls, simple robots, etc." -->

The processor in Barbie typewriters that can encrypt is a 4-bit microcontroller.<ref>[https://www.cryptomuseum.com/crypto/mehano/barbie/ Paul Reuvers and Marc Simons. Crypto Museum. "Barbie Typewriter", 2015]</ref>

Several manufacturers used 4-bit microcontrollers in their early electronic games:<ref>{{cite web |title=National Semiconductor COP400 |url=http://seanriddle.com/cop400.html |publisher=Sean Riddle |access-date=24 December 2021}}</ref>
* [[Mattel|Mattel's]] Funtronics Jacks, Red Light Green Light, Tag, Plus One and Dalla$.
* [[Milton Bradley Company|Milton Bradley]] Lightfight and Electronic Battleship 1982. 
* [[Coleco]] Head to Head Basketball.
* National Semiconductor Quiz Kid Racer.
* [[Entex Industries|Entex]] Space Invader.
* [[Texas Instruments]] My Little Computer.<ref>{{cite web |last1=Woerner |first1=Joerg |title=Texas Instruments My Little Computer |url=http://www.datamath.org/Edu/MyLittleComputer.htm |website=Datamath Calculator Museum |access-date=19 June 2024}}</ref>
Western Digital used a 4-bit microcontroller as the basis for their WD2412 time-of-day clock.<ref>{{cite web |title=1983 Components Catalog |url=http://www.bitsavers.org/components/westernDigital/_dataBooks/1983_Western_Digital_Components_Catalog.pdf |page=621 |publisher=Western Digital |access-date=24 December 2021}}</ref>

The [[Grundy Newbrain]] computer uses a 4-bit microcontroller to manage its keyboard, tape I/O, and its built-in 16 character [[Vacuum fluorescent display|VF]] alphanumeric display.<ref>{{cite web |title=COP420 4-Bit Processor - Newbrain |url=https://www.newbrainemu.eu/el/specifications/newbrain/cop420-4-bit-processor.html |access-date=30 December 2021}}</ref>

== Details ==
{{Main|Nibble}}

With 4 bits, it is possible to create 16 different values. All single-digit [[hexadecimal]] numbers can be written with four bits.

[[Binary-coded decimal]] is a digital encoding method for numbers using decimal notation, with each decimal digit represented by four bits.

== List of 4-bit processors ==
[[File:National Semiconductor MM5700CA D Microprocessor.jpg|thumb|upright|National Semiconductor MM5700CA/D [[bit-serial]] 4-bit microcontroller]]

* [[Intel 4004]] (first 4-bit microprocessor from 1971, though [[Four-Phase Systems]] AL1 from 1969 is older, discontinued 1981)
* [[Intel 4040]] (discontinued 1981)
* [[TMS 1000]] (the first high-volume commercial microcontroller, from 1974, after Intel 4004; now discontinued<!-- for sure, and when?-->)
* [[Atmel]] [[MARC4]] core<ref name="Atmel_MARC4_Image" /><ref name="Atmel_MARC4_Product" /> (discontinued because of <!--Reason for EOL: -->Low demand. "Last ship date: 7 March 2015"<ref name="Atmel_EOL" />)
* [[Samsung]] S3C7 (KS57 Series) 4-bit microcontrollers (RAM: 512 to 5264 nibbles, 6&nbsp;MHz clock)
* [[Toshiba]] [[TLCS-47]] series
* [[HP Saturn]]<!-- and [[HP Saturn+|Saturn+]] series --> <!-- The HP "Saturn+" is not a real microprocessor but instead a Saturn emulator running on an ARM microprocessor -->
* [[NEC]] [[μPD75X]]
* NEC [[μCOM-4]]
* NEC (now [[Renesas]]) μPD612xA (discontinued), μPD613x, [[μPD6x]]<ref name="RenesasPD67" /><ref name="Renesas_uPD6P9" /> and [[μPD1724x]]<ref name="Renesas_uPD17240" /> infrared remote control transmitter microcontrollers<ref name="Renesas_Remote" /><ref name="Necel_ROMless" />
* [[EM Microelectronic-Marin]] EM6600 family,<ref name="Cravotta" /> EM6580,<ref name="EM6580_1" /><ref name="EM6580_2" /> EM6682,<ref name="EM6682" /> etc.
* Epson [[S1C63]] family
* [[National Semiconductor]] "COPS I" and "COPS II" ("[[COP400]]") 4-bit microcontroller families<ref>{{cite web |url=http://www.cpushack.com/2014/09/27/national-semiconductor-the-cop-before-the-cops/ |title=National Semiconductor: The COP before the COPS |last=Culver |first=John |date=September 27, 2014 |website=www.cpushack.com |publisher=<!-- N/A --> |access-date=May 28, 2020 |quote=<!-- N/A -->}}</ref>
* [[National Semiconductor]] MAPS MM570X
* [[Sharp Electronics|Sharp]] SM590/SM591/SM595<ref name="Sharp_1990" />{{rp|26–34}}
* Sharp SM550/SM551/SM552<ref name="Sharp_1990" />{{rp|36–48}}
* Sharp SM578/SM579<ref name="Sharp_1990" />{{rp|49–64}}
* Sharp SM5E4<ref name="Sharp_1990" />{{rp|65–74}}
* Sharp LU5E4POP<ref name="Sharp_1990" />{{rp|75–82}}
* Sharp SM5J5/SM5J6<ref name="Sharp_1990" />{{rp|83–99}}
* Sharp SM530<ref name="Sharp_1990" />{{rp|100–109}}
* Sharp SM531<ref name="Sharp_1990" />{{rp|110–118}}
* Sharp SM500<ref name="Sharp_1990" />{{rp|119–127}} (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
* Sharp SM5K1<ref name="Sharp_1990" />{{rp|128–140}}
* Sharp SM4A<ref name="Sharp_1990" />{{rp|141–148}}
* Sharp SM510<ref name="Sharp_1990" />{{rp|149–158}} (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
* Sharp SM511/SM512<ref name="Sharp_1990" />{{rp|159–171}} (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
* Sharp SM563<ref name="Sharp_1990" />{{rp|172–186}}

== See also ==
* [[GMC-4]]
* [[Hitachi HD44780 LCD controller]]
* Intel's [[Low Pin Count|LPC]] (low-pin-count) bus/interface for 4-bit communication
** Its successor for modern computers, Intel's [[Enhanced Serial Peripheral Interface]] (eSPI), allows 1-bit, 2-bit, and 4-bit communication

== References ==
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<ref name="Hofstra_History">{{cite web |title=History in the Computing Curriculum |url=http://www.hofstra.edu/pdf/comphist_9812tla6.pdf |access-date=2017-06-22 |archive-url=https://web.archive.org/web/20110719211222/http://www.hofstra.edu/pdf/CompHist_9812tla6.PDF |archive-date=2011-07-19 |url-status=dead}}</ref>
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<ref name="ISOIEC9899_1999_2">{{cite book |title=ISO/IEC 9899:1999 specification |at=p. 37, §&nbsp;6.2.6.1 (4) |url=https://c0x.shape-of-code.com/6.2.6.1.html |access-date=2023-07-24}}</ref>
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<ref name="Atmel_EOL">{{cite web |url=http://www.atmel.com/images/he140901.pdf |title=Product End-of-Life (EOL) Notification |date=2014-03-07 |publisher=[[Atmel]] |archive-url=https://web.archive.org/web/20160807174435/http://www.atmel.com/images/he140901.pdf |archive-date=2016-08-07 |url-status=dead}}</ref>
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<ref name="Renesas_Remote">{{Cite web|url=http://documentation.renesas.com/doc/DocumentServer/U14372EJ5V0PF00.pdf|title=Microcontrollers for Remote Controllers|website=documentation.renesas.com|archive-url=https://web.archive.org/web/20131219191519/http://documentation.renesas.com/doc/DocumentServer/U14372EJ5V0PF00.pdf|archive-date=2013-12-19}}</ref>
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<ref name="Cravotta">{{cite web |author-first=Robert |author-last=Cravotta |url=http://www.embeddedinsights.com/directory/epd-downloads.php |title=Embedded Processing Directory}}</ref>
<ref name="EM6580_1">{{cite web |url=http://www.emmarin.com/Products.asp?IdProduct=215 |title=EM6580 |access-date=2013-05-12 |archive-url=https://web.archive.org/web/20131219221418/http://www.emmarin.com/Products.asp?IdProduct=215 |archive-date=2013-12-19 |url-status=dead}}</ref>
<ref name="EM6580_2">{{Cite web|url=https://www.emmicroelectronic.com/product/multi-io/em6580|title=EM6580}}</ref>
<ref name="EM6682">{{Cite web|url=https://www.emmicroelectronic.com/product/multi-io/em6682|title=EM6682}}</ref>
<ref name="Sharp_1990">{{cite book |url=http://bitsavers.org/components/sharp/_dataBooks/1990_Sharp_Microcomputers_Data_Book.pdf |title=Sharp Microcomputers Data Book |date=September 1990 |access-date=2018-01-05}}</ref>
}}

== External links ==
* [http://www.hpmuseum.org/saturn.htm Saturn CPU]
* {{cite web |url=http://www.epson.jp/device/semicon_e/product/mcu/high_4bit/ |archive-url=https://web.archive.org/web/20130729191831/http://www.epson.jp/device/semicon_e/product/mcu/high_4bit/ |archive-date=2013-07-29 |url-status=dead |website=Epson |title=Products: High Performance 4-bit Microcontrollers (S1C63 family)}}
* [http://www.embeddedinsights.com/channels/2010/12/10/considerations-for-4-bit-processing/ Considerations for 4-bit processing]

{{CPU technologies}}

[[Category:Data unit]]