Instruction (computer science)
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 postition.
*
Data (computing)*
Machine language
