{{Otheruses3|Instruction}}
In Computer_science, an '''instruction''' typically refers to a single operation of a processor within a Computer_architecture.
The types of instruction allowed are defined and determined within the particular platform's Instruction_set_architecture (ISA), which also determines register sources and destination operands, and perhaps an immediate field. Machine instructions are numbers represented in binary Assembly_code is a developed form of short code. A portion (field) of the instruction designates the operation to be done and is called an Opcode; since the numeric value of this is not very meaningful to humans, a corresponding short abbreviation is used by Programmers. The size, or "width" of an instruction depends on the architecture of the platform, but it is usually from 4 to 64 Bits wide. The following is an example of a X86 instruction in symbolic Assembler notation:
:SHL AX, 01
'''SHL''' is called the operation, and '''AX''', '''01''' are called Operands. '''AX''' is the name of a register, '''01''' is a constant. In this example, '''SHL''' is a Mnemonic abbreviation for "shift left". The instruction causes the value in '''AX''' to be shifted left by '''01''' bit position.
==See also==
*Command_(computing)
*Data_(computing)
*Machine_language
Category:Machine_code
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