4-bit

In computer science, 4-bit is an adjective used to describe integers that are at most 4 bits wide, or to describe CPU architectures based on registers, address buses, or data buses of that size.

The term "4-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 4-bit CPU can process 4 bits at a time.
• Memory addresses.
• Data transferred on each read or write of the memory.

The Intel 4004, the world's first single-chip microprocessor, was a 4-bit CPU.