|Computer architecture bit widths|
|Binary floating-point precision|
|Decimal floating-point precision|
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, 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, 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 4-bit processors were programmed in assembly language or Forth, e.g. "MARC4 Family of 4 bit Forth CPU" 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, and that all data types other than bitfields have a size that is a multiple of the character size).
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.
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, sometimes called "nybble-serial".
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.
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.
While 32- and 64-bit processors are more prominent in modern consumer electronics, 4-bit CPUs can as of 2021[update] 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), 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". Other typical uses include coffee makers, infrared remote controls, and security alarms.
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
- Intel 4040
- TMS 1000
- Atmel MARC4 core – (discontinued: "Last ship date: 7 March 2015")
- 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 and μPD1724x infrared remote control transmitter microcontrollers
- EM Microelectronic-Marin EM6600 family, EM6580, EM6682, etc.
- Epson S1C63 family
- National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families
- National Semiconductor MAPS MM570X
- Sharp SM590/SM591/SM595:26–34
- Sharp SM550/SM551/SM552:36–48
- Sharp SM578/SM579:49–64
- Sharp SM5E4:65–74
- Sharp LU5E4POP:75–82
- Sharp SM5J5/SM5J6:83–99
- Sharp SM530:100–109
- Sharp SM531:110–118
- Sharp SM500:119–127 (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
- Sharp SM5K1:128–140
- Sharp SM4A:141–148
- Sharp SM510:149–158 (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
- Sharp SM511/SM512:159–171 (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
- Sharp SM563:172–186
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bigadder.qasm: Quantum ripple-carry adder. 8-bit adder made out of 2 4-bit adders from adder.qasm.
- 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.
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- "MARC4 4-bit Microcontrollers - Programmer's Guide" (PDF). Atmel. Archived from the original (PDF) on 2014-12-15. Retrieved 2014-01-14.
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- "Product End-of-Life (EOL) Notification" (PDF). Atmel. 2014-03-07. Archived from the original (PDF) on 2016-08-07.
- "μPD6P9 4-bit single-chip microcontroller for infrared remote control transmission" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-03-27.
- "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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- Sharp Microcomputers Data Book (PDF). September 1990. Retrieved 2018-01-05.
- Saturn CPU
- "Products: High Performance 4-bit Microcontrollers (S1C63 family)". Epson. Archived from the original on 2013-07-29.
- Considerations for 4-bit processing