microinstruction

microinstruction

[¦mī·krō·in′strək·shən]

(computer science)

The portion of a microprogram that specifies the operation of individual computing elements and such related subunits as the main memory and the input/output interfaces; usually includes a next-address field that eliminates the need for a program counter.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

microinstruction

A single instruction in microcode. It is the most elementary instruction in the computer, such as moving the contents of a register to the arithmetic logic unit (ALU). It takes several microinstructions to carry out one complex machine instruction (CISC). Also called a "micro-op" or "µop," microinstructions differ within the same computer family and even the same vendor. For example, although all are x86 chips, the microcode for Intel's Pentium 4, Pentium M and AMD's Athlon are not the same. The software programmer never sees microinstructions, and they are not documented for the public. See microcode.

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