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8-bit
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{{about|computer architecture}}{{multiple issues|{{refimprove|date=October 2009}}{{primary sources|date=August 2012}}{{Original research|date=May 2019}}}}{{N-bit|8|(1 octet)}} 8-bit is also a generation of microcomputers in which 8-bit microprocessors were the norm.The IBM System/360 introduced byte-addressable memory with 8-bit bytes, as opposed to bit-addressable or decimal digit-addressable or word-addressable memory, although its general purpose registers were 32 bits wide, and addresses were contained in the lower 24 bits of those addresses. Different models of System/360 had different internal data path widths; the IBM System/360 Model 30 (1965) implemented the 32-bit System/360 architecture, but had an 8 bit native path width, and performed 32-bit arithmetic 8 bits at a time.JOURNAL, Amdahl, G. M., Blaauw, G. A., Gerrit Blaauw, Brooks, F. P., Fred Brooks, 1964, Architecture of the IBM System/360,weblink no, IBM Journal of Research and Development, 8, 2, 87–101, 10.1147/rd.82.0087,weblink 2017-08-10, Gene Amdahl, The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system; it had 8-bit data words and 16-bit addresses. The Zilog Z80 (compatible with the 8080) and the Motorola 6800 were also used in similar computers. The Z80 and the MOS Technology 6502 8-bit CPUs were widely used in home computers and second- and third-generation game consoles of the 1970s and 1980s. Many 8-bit CPUs or microcontrollers are the basis of today's ubiquitous embedded systems.

Details

There are 28 (256) different possible values for 8 bits. When unsigned, it has possible values ranging from 0 to 255; when signed, it has -128 to 127.Eight-bit CPUs use an 8-bit data bus and can therefore access 8 bits of data in a single machine instruction. The address bus is typically a double octet wide (i.e. 16-bit), due to practical and economical considerations. This implies a direct address space of only 64 kB on most 8-bit processors.

Notable 8-bit CPUs

The first commercial 8-bit processor was the Intel 8008 (1972) which was originally intended for the Datapoint 2200 intelligent terminal. Most competitors to Intel started off with such character oriented 8-bit microprocessors. Modernized variants of these 8-bit machines are still one of the most common types of processor in embedded systems.Another notable 8-bit CPU is the MOS Technology 6502; it, and variants of it, were used in a number of personal computers such as the Apple I and Apple II, the Atari 8-bit family, the BBC Micro, and the Commodore PET and Commodore VIC-20, and in a number of video game consoles such as the Atari 2600 and the Nintendo Entertainment System.{|class="wikitable sortable"|+ Early or popular 8-bit processors (incomplete)! Manufacturer! Processor! Year! Comment
Intel 8008>8008 1972 Datapoint 2200 compatible
Signetics>Signetics 2650>2650 1973
Intel 8080>8080 1974 8008 source compatible
Motorola>Motorola 6800>6800 1974
Fairchild Semiconductor>FairchildFairchild F8 >|
MOS Technology>MOSMOS Technology 6502 >| Similar to 6800, but incompatible
Microchip Technology>MicrochipPIC microcontroller >|Harvard architecture microcontroller
EA9002 >| 8-bit data, 12-bit addressing
RCA>RCA 1802>1802 1976
Zilog>Zilog Z80>Z80 1976 8080 binary compatible
Intel 8085>8085 1977 8080 binary compatible
Motorola 6809>6809 1978 6800 source compatible
Zilog Z8>Z8 1978 Harvard architecture microcontroller
Intel 8051>8051 1980 Harvard architecture microcontroller
MOS Technology 6510>6510 1982 Enhanced 6502 custom-made for use in the Commodore 64
Ricoh>Ricoh 2A03>2A03 1982 6502 clone minus BCD instructions for the Nintendo Entertainment System
Zilog Z180>Z180 1985 Z80 binary compatible
Freescale 68HC11>68HC11 1985
Atmel>Atmel AVR>AVR 1996
Zilog eZ80>EZ80 1999 Z80 binary compatible
Infineon >XC800 family>XC800 2005
Freescale Semiconductor>Freescale Freescale 68HC08 >|
Hudson Soft>HudsonHudson Soft HuC6280 >|
Motorola 6800 family>6803
NEC>NEC 78K0>78K0HTTP://WWW.AM.NECEL.COM/MICRO/PRODUCT/ALL_8_GENERAL.HTML/>TITLE=NEC 78K0FIRST=WEBSITE=NEC>ARCHIVE-URL=HTTPS://WEB.ARCHIVE.ORG/WEB/20081028210428/HTTP://WWW.AM.NECEL.COM/MICRO/PRODUCT/ALL_8_GENERAL.HTML/DEAD-URL=YES|

References

{{Reflist}}{{CPU technologies}}

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