4-bit computing

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In computer architecture, 4-bit integers, or other data units are those that are 4 bits wide. Also, 4-bit CPU and ALU architectures are those that are based on registers, or data buses of that size. Memory addresses (and thus address buses) for 4-bit CPUs are generally much larger than 4-bit (since only 16 memory locations would be very restrictive), such as 12-bit or more, while they could in theory be 8-bit. A group of four bits is also called a nibble and has 24 = 16 possible values.

Some of the first microprocessors had a 4-bit word length and were developed around 1970. Traditional (non-quantum) 4-bit computers are by now obsolete, while recent quantum computers are 4-bit,[1][2] but also based on qubits, such as the IBM Q Experience. See also: Bit slicing#Bit-sliced quantum computers.

The first commercial microprocessor was the binary-coded decimal (BCD-based) Intel 4004,[3][4] 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.

The Texas Instruments TMS 1000 (1974) was a 4-bit CPU; it had a Harvard architecture, with an on-chip instruction ROM, 8-bit-wide instructions and an on-chip data RAM with 4-bit words.[5]

The 4-bit processors were programmed in assembly language or Forth, e.g. "MARC4 Family of 4 bit Forth CPU"[6] 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 requires that the size of the char data type be at least 8 bits,[7] and that all data types other than bitfields have a size that is a multiple of the character size[8][9][10]).

The 1970s saw the emergence of 4-bit software applications for mass markets like pocket calculators. During the 1980s 4-bit microprocessor 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 chip.

The Zilog Z80, although it is an 8-bit microprocessor, has a 4-bit ALU.[11][12]

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,[13] sometimes called "nybble-serial".[14]

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.[15][16][17]

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.[18]


While 32- and 64-bit processors are more prominent in modern consumer electronics, 4-bit CPUs can as of 2021 be bought online at down to $0.23 (in bulk for 1000 units, or at $0.70 for one of the same kind or $2.55 for a different kind),[19][20] while an 8-bit microcontroller can be bought for $0.24 for a single one (also obsolete; and a non-obsolete 8-bit CPUs can be bought for $0.30 per unit, for 702 units at $210.60), a fraction of the 4-bit price, and even a single modern 32-bit microcontroller can be bought for $0.24 so it's unclear if 4-bit CPUs are still used for anything else than for replacement parts. For example, 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]


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.

Binary Octal Decimal Hexadecimal
0000 0 0 0
0001 1 1 1
0010 2 2 2
0011 3 3 3
0100 4 4 4
0101 5 5 5
0110 6 6 6
0111 7 7 7
1000 10 8 8
1001 11 9 9
1010 12 10 A
1011 13 11 B
1100 14 12 C
1101 15 13 D
1110 16 14 E
1111 17 15 F

List of 4-bit processors[edit]

16-pin DIP
Intel C4004
infrared remote control PCB
an infrared remote control transmitter controlled by a NEC D63GS 4-bit microcontroller
20-pin PSOP
NEC D63GS: a 4-bit microcontroller for infrared remote control transmission
card-edge PCB
Olympia CD700 Desktop Calculator using the National Semiconductor MAPS MM570X bit-serial 4-bit microcontroller
16-pin DIP
National Semiconductor MM5700CA/D bit-serial 4-bit microcontroller

See also[edit]


  1. ^ "Qiskit/openqasm". GitHub. Retrieved 2020-11-16. bigadder.qasm: Quantum ripple-carry adder. 8-bit adder made out of 2 4-bit adders from adder.qasm.
  2. ^ Cross, Andrew W.; Bishop, Lev S.; Smolin, John A.; Gambetta, Jay M. (2017-07-13). "Open Quantum Assembly Language". arXiv:1707.03429 [quant-ph]. The only storage types of Open QASM (version 2.0) are classical and quantum registers, which are one-dimensional arrays of bits and qubits, respectively.
  3. ^ Mack, Pamela E. (2005-11-30). "The Microcomputer Revolution". Retrieved 2009-12-23.
  4. ^ "History in the Computing Curriculum" (PDF). Archived from the original (PDF) on 2011-07-19. Retrieved 2017-06-22.
  5. ^ TMS 1000 Series Data Manual (PDF). Texas Instruments. December 1976. Retrieved 2013-07-20.
  6. ^ "Forth Chips". www.ultratechnology.com.
  7. ^ ISO/IEC 9899:1999 specification. p. 20, §
  8. ^ ISO/IEC 9899:1999 specification. p. 37, § (4).
  9. ^ Cline, Marshall. "C++ FAQ: the rules about bytes, chars, and characters".
  10. ^ "4-bit integer". cplusplus.com. Retrieved 2014-11-21.
  11. ^ 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).
  12. ^ Shirriff, Ken. "The Z-80 has a 4-bit ALU".
  13. ^ Hendrie, Gardner (2002-11-22). "Oral History of Edson (Ed) D. de Castro" (PDF) (Interview). p. 44.
  14. ^ "Nova 1200".
  15. ^ "The Saturn Processor". Retrieved 2015-12-23.
  16. ^ "Guide to the Saturn Processor". Retrieved 2014-01-14.
  17. ^ "Introduction to Saturn Assembly Language". Retrieved 2014-01-14.
  18. ^ "Desk Electronic Calculators: Casio AL-1000".
  19. ^ "4570 NEC | IC Chips". UTSOURCE. Retrieved 2021-03-29.
  20. ^ "UPD6700GH-3B7 Renesas,10+ | IC Chips". UTSOURCE. Retrieved 2020-07-02.
  21. ^ "Cateye Commuter Manual" (PDF). Retrieved 2014-02-11.
  22. ^ a b "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.
  23. ^ Haskell, Richard. "Introduction to Digital Logic and Microprocessors (Lecture 12.2)". Retrieved 2014-02-11.
  24. ^ "MARC4 4-bit Microcontrollers - Programmer's Guide" (PDF). Atmel. Archived from the original (PDF) on 2014-12-15. Retrieved 2014-01-14.
  25. ^ "MARC4 4-Bit Architecture". Atmel. Archived from the original on 2009-05-31.
  26. ^ "Product End-of-Life (EOL) Notification" (PDF). Atmel. 2014-03-07. Archived from the original (PDF) on 2016-08-07.
  27. ^ "μPD6P9 4-bit single-chip microcontroller for infrared remote control transmission" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-03-27.
  28. ^ "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.
  29. ^ "Microcontrollers for Remote Controllers" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2013-12-19.
  30. ^ "Mask ROM/ROMless Products 4/8bit Remote Control". Archived from the original on 2008-10-28.
  31. ^ Cravotta, Robert. "Embedded Processing Directory".
  32. ^ "EM6580". Archived from the original on 2013-12-19. Retrieved 2013-05-12.
  33. ^ "EM6580 low power Flash 4-bit microcontroller".
  34. ^ "EM6682".
  35. ^ Culver, John (2014-09-27). "National Semiconductor: The COP before the COPS". www.cpushack.com. Retrieved 2020-05-28.
  36. ^ a b c d e f g h i j k l m n Sharp Microcomputers Data Book (PDF). September 1990. Retrieved 2018-01-05.

External links[edit]