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| 1-bit | 4-bit | 8-bit | 12-bit | 16-bit | 18-bit | 24-bit | 31-bit | 32-bit | 36-bit | 48-bit | 60-bit | 64-bit | 128-bit |
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| 8-bit | 16-bit | 32-bit | 64-bit | ||||||||||
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| bit nibble octet byte | |||||||||||||
| halfword word dword qword | |||||||||||||
| IEEE floating-point standard | |||||||||||||
| Single precision floating-point format (32-bit) Double precision floating-point format (64-bit) Quadruple precision floating-point format (128-bit) | |||||||||||||
In computer architecture, 8-bit integers, memory addresses, or other data units are those that are at most 8 bits (1 octet) wide. Also, 8-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 8-bit is also a term given to a generation of computers in which 8-bit processors are the norm.
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. 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 game consoles of the '70s and '80s. Many 8-bit CPUs or microcontrollers are the basis of today's ubiquitous embedded systems.
There are 28 (256) possible values for 8 bits.
The first microprocessors had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the BCD-based Intel 4004 (1971), developed for calculator applications. The first commercial 8-bit processor was the Intel 8008 (1972) which was originally intended for intelligent terminals. 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.
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 KiB on most 8-bit processors.
Early and/or popular 8-bit processors (incomplete):
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