4-bit computing

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.

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 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]

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]

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.

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)
• Atmel MARC4 core[23][24] – (discontinued because of Low demand. "Last ship date: 7 March 2015"[25])
• 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, μPD6x[20][26] and μPD1724x[27] infrared remote control transmitter microcontrollers[28][29]
• EM Microelectronic-Marin EM6600 family,[30] EM6580,[31][32] EM6682,[33] etc.
• Epson S1C63 family
• National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families[34]
• National Semiconductor MAPS MM570X
• Sharp SM590/SM591/SM595[35]^: 26–34
• Sharp SM550/SM551/SM552[35]^: 36–48
• Sharp SM578/SM579[35]^: 49–64
• Sharp SM5E4[35]^: 65–74
• Sharp LU5E4POP[35]^: 75–82
• Sharp SM5J5/SM5J6[35]^: 83–99
• Sharp SM530[35]^{: 100–109}
• Sharp SM531[35]^{: 110–118}
• Sharp SM500[35]^{: 119–127} (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
• Sharp SM5K1[35]^{: 128–140}
• Sharp SM4A[35]^{: 141–148}
• Sharp SM510[35]^{: 149–158} (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
• Sharp SM511/SM512[35]^{: 159–171} (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
• Sharp SM563[35]^{: 172–186}

• GMC-4
• Hitachi HD44780
• Low Pin Count for 4-bit communication
  • Its successor for modern computers, Intel's Enhanced Serial Peripheral Interface (eSPI), allows 1-bit, 2-bit, or 4-bit communication

• Saturn CPU
• "Products: High Performance 4-bit Microcontrollers (S1C63 family)". Epson. Archived from the original on 2013-07-29.
• Considerations for 4-bit processing