machine instruction

machine instruction

[mə′shēn in‚strək·shən]

(computer science)

A set of digits, binary bits, or characters that a computer can recognize and act upon, and that, when interpreted or decoded, indicates the action to be performed and which operand is to be involved in the action.

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

machine instruction

A directive in the native binary language of the hardware platform it is running in. The anatomy of a machine instruction is an operation code (op code) followed by one or more operand nouns. The op code is the action, while the operands are the data locations in memory to be acted upon or the program location in memory to switch to. There are instructions to INPUT and OUTPUT data, to process data by CALCULATING, COMPARING and COPYING and to go to some other part of the program. There are also instructions that manipulate the CPU's registers, as well as to go to some other part of the program based on the results of the last COMPARE operation (high, low, equal).

The following examples are conceptual and represent what a machine instruction would do. They are not actual instructions. See machine language, assembly language, hardware platform and computer.

OP CODE        OPERANDS(verb)         (the nouns)

 add            amount to total

 compare        search-key to item-1

 if last compare
  was equal,
  go to         routine-A

 copy           from - to

 go to          routine-X

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