operation code

programming (Or "op code") The part or parts of a machinelanguage instruction which determines what kind of action the

computer should take, e.g. add, jump, load, store. In any

particular instruction set certain fixed bit positions

within the instruction word contain the op code, others give

parameters such as the addresses or registers involved.

For example, in a 32-bit instruction the most significant

eight bits might be the op code giving 256 possible

operations.

For some instruction sets, certain values in the fixed bit

positions may select a group of operations and the exact

operation may depend on other bits within instruction word or

subsequent words.

When programming in assembly language, the op code is

represented by a readable name called an instructionmnemonic.

(1997-02-14)