4-bit computing

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 , 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]

Uses[]

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]

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

Details[]

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 C4004

an infrared remote control transmitter controlled by a NEC D63GS 4-bit microcontroller

NEC D63GS: a 4-bit microcontroller for infrared remote control transmission

Olympia CD700 Desktop Calculator using the National Semiconductor MAPS MM570X bit-serial 4-bit microcontroller

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

• Intel 4004
• Intel 4040
• TMS 1000
• Atmel core^[25][26] – (discontinued: "Last ship date: 7 March 2015"^[27])
• 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^[22][28] and μPD1724x^[29] infrared remote control transmitter microcontrollers^[30][31]
• EM Microelectronic-Marin EM6600 family,^[32] EM6580,^[33][34] EM6682,^[35] etc.
• Epson S1C63 family
• National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families^[36]
• National Semiconductor MAPS MM570X
• Sharp SM590/SM591/SM595^[37]:26–34
• Sharp SM550/SM551/SM552^[37]:36–48
• Sharp SM578/SM579^[37]:49–64
• Sharp SM5E4^[37]:65–74
• Sharp LU5E4POP^[37]:75–82
• Sharp SM5J5/SM5J6^[37]:83–99
• Sharp SM530^{[37]:100–109}
• Sharp SM531^{[37]:110–118}
• Sharp SM500^{[37]:119–127} (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
• Sharp SM5K1^{[37]:128–140}
• Sharp SM4A^{[37]:141–148}
• Sharp SM510^{[37]:149–158} (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
• Sharp SM511/SM512^{[37]:159–171} (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
• Sharp SM563^{[37]:172–186}

See also[]

• GMC-4
• Hitachi HD44780 - LCD controller with 4-bit mode
• Low Pin Count (LPC)

References[]

External links[]

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