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From Wikipedia, the free encyclopedia

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
16-bit 32-bit 64-bit
Data Sizes
nibble   octet   byte   word   dword   qword

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 were the norm.

Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their address space is limited to 64 KB. This is not a "natural law", however, so there are exceptions.

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.

As of 2009, about 55% of all CPUs sold in the world are 8-bit microcontrollers or microprocessors.

Why 8 bits?

4-bit microprocessors were developed in the early 1970s starting with the Intel 4004. Intel swiftly followed with 8-bit processors, and most competitors to Intel started with 8-bits. Performance and memory limitations meant that 4-bit processors fell out of more demanding applications quickly (4-bit processors are still mass-produced however).

List of 8-bit CPUs

A CPU can be classified on the basis of the data it can access in a single operation. An 8-bit processor can access 8 bits of data in a single operation, as opposed to a 16-bit processor, which can access 16 bits of data in a single operation.

Examples of 8-bit processors (very incomplete):



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary



8-bit (not comparable)


not comparable

none (absolute)

  1. (computing, of a word size, or an integer) Represented using 8 bits (1 byte)

See also


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