Opcode

Part of speech: noun

Definitions

1. A code representing a specific instruction in machine language that the CPU decodes and executes
2. A symbolic representation of an operation in assembly language that dictates what action the processor takes
3. A numerical value identifying a particular operation or command executed by a computer's processor

Etymology: "Opcode" is a plain compound: "op," short for "operation," joined to "code." The "code" half is the familiar sense of a system of symbols standing for something else, here a numeric pattern that stands for an instruction. The "op" half is the older clipping, and the compound describes exactly what the word names: the operation part of a machine instruction, the bit pattern that tells the processor what to do, while the remaining bits typically supply the data or addresses it acts on. The word works as a neat example of how computing vocabulary tends to be built. Engineers needed a short name for one field of an instruction, and they assembled it from existing English parts rather than borrowing from another language. The result is transparent: a reader who has never programmed can still guess the meaning from the two halves.

Synonyms: operation code, instruction code