8-bit

This article is about computer architecture. For other uses, see 8-bit (disambiguation).

Processors
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
Applications
		8-bit		16-bit				32-bit				64-bit
Data sizes
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.

Important 8-bit CPUs

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):

• Intel 8008 (1972 Datapoint 2200 compatible)
• Intel 8080 (1974 8008 source compatible)
• Motorola 6800 (1974)
• MOS Technology 6502 (1975 similar to 6800, but incompatible)
• Zilog Z80 (1976 8080 binary compatible)
• Intel 8085 (1977 8080 binary compatible)
• Zilog Z8 (1978 Harvard architecture microcontroller)
• Motorola 6809 (1978 partially 6800 compatible)
• Intel 8051 (1980 Harvard architecture microcontroller)
• Zilog Z180 (1985 Z80 binary compatible)
• Zilog eZ80 (1999/2001 Z80 binary compatible)
• Motorola 6803
• Freescale 68HC08
• Freescale 68HC11
• RCA 1802
• Hudson Soft HuC6280
• PIC microcontroller
• Atmel AVR family microcontrollers
• NEC 78K0 series * Infineon XC800 family microcontrollers

See also

• History of video game consoles (third generation)
• Vasm, a free assembler