8-bit

In computer science, 8-bit is an adjective used to describe integers that are at most 8 bits (1 octet) wide, or to describe CPU architectures based on registers, address buses, or data buses of that size.

The term "8-bit" can be used to describe the size of any of the following:

• A data unit.
  • A 4-bit unit (a hexadecimal digit) is called a nibble or nybble.
  • An 8-bit unit is called an octet (or a byte).
• A CPU's registers used to hold memory addresses and other data, as well as the ALU that operates on those registers.
  • Data units of that size are called words.
  • A 8-bit CPU can process 8 bits at a time.
• Memory addresses.
• Data transferred on each read or write of the memory.

8-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 kilobytes; this is not a "natural law", however, and thus 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 permutations for 8 bits.