|Computer architecture bit widths|
|Binary floating-point precision|
|Decimal floating-point precision|
In computer architecture, 4-bit integers, memory addresses, 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, address buses, or data buses of that size. 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. The 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. 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.
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.
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). While larger than 4-bit values can be used by combining more than one manually, the language has to support the smaller values used in the combining. If not, assembly is the only option.[dubious ]
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.
While 32- and 64-bit processors are more prominent in modern consumer electronics, 4-bit CPUs continue to be used (usually as part of a microcontroller) in cost-sensitive applications that require minimal computing power. 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.
Use of 4-bit processors has declined relative to 8-bit or even 32-bit processors, as they are hard to find cheaper in general computer suppliers' stores. The simplest kinds are not available in any of them, and others are "non-stock" and more expensive. (A few expensive ones can be found, as of 2014[update], on eBay.)
As of 2015[update], most PC motherboards, especially laptop motherboards, use a 4-bit LPC bus (introduced in 1998) to connect the southbridge to the motherboard firmware flash ROM (UEFI or BIOS) and the Super I/O chip.
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
- TMS 1000
- Intel 4004
- Intel 4040
- Atmel MARC4 core – (discontinued: "Last ship date: March 7, 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 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 1197x8 bit, RAM 40x4 bit, a divider and 56-segment LCD driver circuit)
- Sharp SM5K1:128–140
- Sharp SM4A:141–148
- Sharp SM510:149–158 (ROM 2772x8 bit, RAM 128x4 bit, a divider and 132-segment LCD driver circuit)
- Sharp SM511/SM512:159–171 (ROM 4032X8 bit, RAM 128/142x4 bit, a divider and 136/200-segment LCD driver circuit)
- Sharp SM563:172–186
- TMS 1000 Series Data Manual (PDF). Texas Instruments. December 1976. Retrieved July 20, 2013.
- Mack, Pamela E. (November 30, 2005). "The Microcomputer Revolution". Retrieved December 23, 2009.
- "History in the Computing Curriculum" (PDF). Archived from the original (PDF) on July 19, 2011. Retrieved June 22, 2017.
- "The Saturn Processor". Retrieved December 23, 2015.
- "Guide to the Saturn Processor". Retrieved January 14, 2014.
- "Introduction to Saturn Assembly Language". Retrieved January 14, 2014.
- Forth Chips.
- ISO/IEC 9899:1999 specification. p. 20, § 126.96.36.199.1.
- ISO/IEC 9899:1999 specification. p. 37, § 188.8.131.52 (4).
- Marshall Cline. "C++ FAQ: the rules about bytes, chars, and characters".
- "4-bit integer". cplusplus.com. Retrieved November 21, 2014.
- Masatoshi Shima; Federico Faggin; Ralph Ungermann; Michael Slater (April 27, 2007). "Zilog Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor" (PDF).
- Ken Shirriff. "The Z-80 has a 4-bit ALU".
- "Cateye Commuter Manual" (PDF). Retrieved February 11, 2014.
- "μPD67, 67A, 68, 68A, 69 4-bit single-chip microcontroller for infrared remote control transmission" (PDF).
- Haskell, Richard. "Introduction to Digital Logic and Microprocessors (Lecture 12.2)". Retrieved February 11, 2014.
- "Embedded - Microcontrollers - Integrated Circuits (ICs) - DigiKey". digikey.com. Retrieved April 9, 2018.
- "Other Integrated Circuits - eBay". eBay. Retrieved April 9, 2018.
- "Motorola IC MC14500B / MC14500BCL ( 100% NEW ) - eBay". eBay. Retrieved April 9, 2018.
- "KL1868VE1 Soviet CMOS Clone Matsushita MN15500 4bit MCU - eBay". eBay. Retrieved April 9, 2018.
- Scott Mueller. "Upgrading and Repairing Laptops". 2004. p. 176.
- David S. Lawyer. "Plug-and-Play-HOWTO: LPC Bus" 2007.
- "MARC4 4-bit Microcontrollers - Programmer's Guide" (PDF). Atmel. Archived from the original (PDF) on December 15, 2014. Retrieved January 14, 2014.
- "MARC4 4-Bit Architecture". Atmel. Archived from the original on May 31, 2009.
- "Product End-of-Life (EOL) Notification" (PDF). Atmel. March 7, 2014. Archived from the original (PDF) on August 7, 2016.
- "μPD6P9 4-bit single-chip microcontroller for infrared remote control transmission" (PDF).
- "μPD17240, 17241, 17242, 17243, 17244, 17245, 17246 4-bit single-chip microcontrollers for small general-purpose infrared remote control transmitters" (PDF).
- "Microcontrollers for Remote Controllers" (PDF).
- "Mask ROM/ROMless Products 4/8bit Remote Control". Archived from the original on October 28, 2008.
- Robert Cravotta. "Embedded Processing Directory"
- "EM6580". Archived from the original on December 19, 2013. Retrieved May 12, 2013.
- "EM6580 low power Flash 4-bit microcontroller"
- Sharp Microcomputers Data Book (PDF). September 1990. Retrieved January 5, 2018.
- Saturn CPU
- "Products: High Performance 4-bit Microcontrollers [ S1C63 family ]". Epson. Archived from the original on July 29, 2013.
- Considerations for 4-bit processing