4-bit computing is the use of computer architectures in which integers and other data units are 4 bits wide. 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses of that size. A group of four bits is also called a nibble and has 24 = 16 possible values.

4-bit processors were widely used in electronic calculators and other roles where decimal math was used, like electronic cash registers, 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 circuits 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 By the 1990s, most such uses had been replaced by general purpose binary designs.


20-pin PSOP – NEC D63GS: a 4-bit microcontroller for infrared remote control transmission
16-pin DIP – Intel C4004
Olympia CD700 Desktop Calculator using the National Semiconductor MAPS MM570X bit-serial 4-bit microcontroller
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.[1]

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,[2][3] 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).[1] 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.[4]

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.[5]

The 4-bit processors were programmed in assembly language or Forth, e.g. "MARC4 Family of 4 bit Forth CPU"[6] (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,[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 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, 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]


One bicycle computer specifies that it uses a "4 bit, 1-chip microcomputer".[19] Other typical uses include coffee makers, infrared remote controls,[20] and security alarms.[21]

The processor in Barbie typewriters that can encrypt is a 4-bit microcontroller.[22]


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

National Semiconductor MM5700CA/D bit-serial 4-bit microcontroller

See also


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  5. ^ "Rockwell PPS-4".
  6. ^ "Forth Chips". www.ultratechnology.com.
  7. ^ ISO/IEC 9899:1999 specification. p. 20, § Retrieved 2023-07-24.
  8. ^ ISO/IEC 9899:1999 specification. p. 37, § (4). Retrieved 2023-07-24.
  9. ^ Cline, Marshall. "C++ FAQ: the rules about bytes, chars, and characters".
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  22. ^ Paul Reuvers and Marc Simons. Crypto Museum. "Barbie Typewriter", 2015
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  24. ^ "MARC4 4-Bit Architecture". Atmel. Archived from the original on 2009-05-31.
  25. ^ "Product End-of-Life (EOL) Notification" (PDF). Atmel. 2014-03-07. Archived from the original (PDF) on 2016-08-07.
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  27. ^ "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.
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  33. ^ "EM6682".
  34. ^ Culver, John (2014-09-27). "National Semiconductor: The COP before the COPS". www.cpushack.com. Retrieved 2020-05-28.
  35. ^ 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.