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In computing, an opcode prefix is an numeric value that alters the function of a following opcode.[1] On some instruction set architectures multiple opcode prefixes are allowed sequentially, with all combining to alter the subsequent opcode. The opcode prefix is a portion of a larger machine language instruction that specifies the operation to be performed.
In addition to the opcode, some instructions specify the operands the operation will act upon. Opcode prefixes may alter the number or size of the operands.
RISC processors do not use opcode prefixes.
- ^ Tanenbaum, Andrew S; Austin, Todd (2013). Structured Computer Organization (Sixth ed.). Pearson Education, Inc. p. 367. ISBN 0-13-291652-5.
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