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4-bit computing
Computer architecture bit width

4-bit computing involves computer architectures where data units like integers are 4 bits wide, forming a nibble with 16 possible values (0–15). Such architectures include early 4-bit CPUs used in electronic calculators and devices like microwave oven timers, benefiting from 4-bit binary-coded decimal digits. While mostly obsolete today, 4-bit values remain relevant in decimal-centric applications and are gaining interest for AI and large-language models. Early processors like the Intel 4004 used 4-bit data but larger address buses. Designs like the 1980s HP Saturn processed multiple 4-bit values in parallel, but by the 1990s, wider, general-purpose architectures predominated.

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History

A 4-bit processor may seem limited, but it is a good match for calculators, where each decimal digit fits into four bits.2

Some of the first microprocessors had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the binary-coded decimal (BCD-based) Intel 4004,34 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).5 It contained a 4-bit 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.6

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.7

The 4-bit processors were programmed in assembly language or Forth, e.g. "MARC4 Family of 4 bit Forth CPU"8 (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for microcontrollers, 8-bit and larger), such as the C programming language, do not support 4-bit data types (C, and C++, and more languages require that the size of the char data type be at least 8 bits,9 and that all data types other than bitfields have a size that is a multiple of the character size101112).

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 games 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 Am2901 or 74181.

The Zilog Z80 (discontinued in 2024), although it is an 8-bit microprocessor, has a 4-bit ALU.1314

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,15 sometimes called "nybble-serial".16

The HP Saturn processors, used in many Hewlett-Packard calculators between 1984 and 2003 (including the HP 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.171819

In addition, some early calculators – such as the 1967 Casio AL-1000, the 1972 Sinclair Executive, and the aforementioned 1984 HP Saturn – had 4-bit datapaths that accessed their registers 4 bits (one BCD digit) at a time.20

Uses

One bicycle computer specifies that it uses a "4 bit, 1-chip microcomputer".21 Other typical uses include coffee makers, infrared remote controls,22 and security alarms.23

The processor in Barbie typewriters that can encrypt is a 4-bit microcontroller.24

Several manufacturers used 4-bit microcontrollers in their early electronic games:25

  • Mattel's Funtronics Jacks, Red Light Green Light, Tag, Plus One and Dalla$.
  • Milton Bradley Lightfight and Electronic Battleship 1982.
  • Coleco Head to Head Basketball.
  • National Semiconductor Quiz Kid Racer.
  • Entex Space Invader.
  • Texas Instruments My Little Computer.26

Western Digital used a 4-bit microcontroller as the basis for their WD2412 time-of-day clock.27

The Grundy Newbrain computer uses a 4-bit microcontroller to manage its keyboard, tape I/O, and its built-in 16 character VF alphanumeric display.28

Details

Main article: 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

  • 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)
  • Atmel MARC4 core2930 (discontinued because of Low demand. "Last ship date: 7 March 2015"31)
  • Samsung S3C7 (KS57 Series) 4-bit microcontrollers (RAM: 512 to 5264 nibbles, 6 MHz clock)
  • Toshiba TLCS-47 series
  • HP Saturn
  • NEC μPD75X
  • NEC μCOM-4
  • NEC (now Renesas) μPD612xA (discontinued), μPD613x, μPD6x3233 and μPD1724x34 infrared remote control transmitter microcontrollers3536
  • EM Microelectronic-Marin EM6600 family,37 EM6580,3839 EM6682,40 etc.
  • Epson S1C63 family
  • National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families41
  • National Semiconductor MAPS MM570X
  • Sharp SM590/SM591/SM59542: 26–34 
  • Sharp SM550/SM551/SM55243: 36–48 
  • Sharp SM578/SM57944: 49–64 
  • Sharp SM5E445: 65–74 
  • Sharp LU5E4POP46: 75–82 
  • Sharp SM5J5/SM5J647: 83–99 
  • Sharp SM53048: 100–109 
  • Sharp SM53149: 110–118 
  • Sharp SM50050: 119–127  (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
  • Sharp SM5K151: 128–140 
  • Sharp SM4A52: 141–148 
  • Sharp SM51053: 149–158  (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
  • Sharp SM511/SM51254: 159–171  (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
  • Sharp SM56355: 172–186 

See also

References

  1. Liu, Shih-Yang; Liu, Zechun; Huang, Xijie; Dong, Pingcheng; Cheng, Kwang-Ting (2023). "LLM-FP4: 4-Bit Floating-Point Quantized Transformers". Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing. pp. 592–605. arXiv:2310.16836. doi:10.18653/v1/2023.emnlp-main.39. /wiki/ArXiv_(identifier) ↩

  2. Ken Shirriff. "Reverse engineering RAM storage in early Texas Instruments calculator chips". https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html ↩

  3. Mack, Pamela E. (2005-11-30). "The Microcomputer Revolution". Retrieved 2009-12-23. http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec122/micro.htm ↩

  4. "History in the Computing Curriculum" (PDF). Archived from the original (PDF) on 2011-07-19. Retrieved 2017-06-22. https://web.archive.org/web/20110719211222/http://www.hofstra.edu/pdf/CompHist_9812tla6.PDF ↩

  5. Ken Shirriff. "Reverse engineering RAM storage in early Texas Instruments calculator chips". https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html ↩

  6. TMS 1000 Series Data Manual (PDF). Texas Instruments. December 1976. Retrieved 2013-07-20. http://blog.kevtris.org/blogfiles/TMS_1000_Data_Manual.pdf ↩

  7. "Rockwell PPS-4". http://www.antiquetech.com/?page_id=796 ↩

  8. "Forth Chips". www.ultratechnology.com. http://www.ultratechnology.com/chips.htm ↩

  9. ISO/IEC 9899:1999 specification. p. 20, § 5.2.4.2.1. Retrieved 2023-07-24. https://c0x.shape-of-code.com/5.2.4.2.1.html ↩

  10. ISO/IEC 9899:1999 specification. p. 37, § 6.2.6.1 (4). Retrieved 2023-07-24. https://c0x.shape-of-code.com/6.2.6.1.html ↩

  11. Cline, Marshall. "C++ FAQ: the rules about bytes, chars, and characters". http://www.parashift.com/c++-faq-lite/bytes-review.html ↩

  12. "4-bit integer". cplusplus.com. Retrieved 2014-11-21. http://www.cplusplus.com/forum/general/51911/ ↩

  13. Shima, Masatoshi; Faggin, Federico; Ungermann, Ralph; Slater, Michael (2007-04-27). "Zilog Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor" (PDF). https://archive.computerhistory.org/resources/text/Oral_History/Zilog_Z80/102658073.05.01.pdf ↩

  14. Shirriff, Ken. "The Z-80 has a 4-bit ALU". http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html ↩

  15. Hendrie, Gardner (2002-11-22). "Oral History of Edson (Ed) D. de Castro" (PDF) (Interview). p. 44. http://archive.computerhistory.org/resources/access/text/2012/07/102702207-05-01-acc.pdf ↩

  16. "Nova 1200" https://rcsri.org/collection/nova-1200/ ↩

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  19. "Introduction to Saturn Assembly Language". Retrieved 2014-01-14. http://www.hpcalc.org/details.php?id=1693 ↩

  20. "Desk Electronic Calculators: Casio AL-1000" http://www.vintagecalculators.com/html/casio_al-1000.html ↩

  21. "Cateye Commuter Manual" (PDF). Retrieved 2014-02-11. http://cateye.com/images/manual/CC-COM10W_ENG_v3.pdf ↩

  22. "μPD67, 67A, 68, 68A, 69 4-bit single-chip microcontroller for infrared remote control transmission" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-01-06. https://web.archive.org/web/20160106205219/http://documentation.renesas.com/doc/DocumentServer/U14935EJ2V1DS00.pdf ↩

  23. Haskell, Richard. "Introduction to Digital Logic and Microprocessors (Lecture 12.2)". Archived from the original on 2014-02-22. Retrieved 2014-02-11. https://web.archive.org/web/20140222063433/http://cse.secs.oakland.edu/haskell/CSE171/Lectures/Fall2004/L12.2%20Microcontrollers.ppt ↩

  24. Paul Reuvers and Marc Simons. Crypto Museum. "Barbie Typewriter", 2015 https://www.cryptomuseum.com/crypto/mehano/barbie/ ↩

  25. "National Semiconductor COP400". Sean Riddle. Retrieved 2021-12-24. http://seanriddle.com/cop400.html ↩

  26. Woerner, Joerg. "Texas Instruments My Little Computer". Datamath Calculator Museum. Retrieved 2024-06-19. http://www.datamath.org/Edu/MyLittleComputer.htm ↩

  27. "1983 Components Catalog" (PDF). Western Digital. p. 621. Retrieved 2021-12-24. http://www.bitsavers.org/components/westernDigital/_dataBooks/1983_Western_Digital_Components_Catalog.pdf ↩

  28. "COP420 4-Bit Processor - Newbrain". Retrieved 2021-12-30. https://www.newbrainemu.eu/el/specifications/newbrain/cop420-4-bit-processor.html ↩

  29. "MARC4 4-bit Microcontrollers – Programmer's Guide" (PDF). Atmel. Archived from the original (PDF) on 2014-12-15. Retrieved 2014-01-14. https://web.archive.org/web/20141215021454/http://www.atmel.com/Images/doc4747.pdf ↩

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  31. "Product End-of-Life (EOL) Notification" (PDF). Atmel. 2014-03-07. Archived from the original (PDF) on 2016-08-07. https://web.archive.org/web/20160807174435/http://www.atmel.com/images/he140901.pdf ↩

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  34. "μPD17240, 17241, 17242, 17243, 17244, 17245, 17246 4-bit single-chip microcontrollers for small general-purpose infrared remote control transmitters" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-03-27. https://web.archive.org/web/20160327182841/http://documentation.renesas.com/doc/DocumentServer/U15002EJ1V1DS00.pdf ↩

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