Instruction Code
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Instruction Code
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An artificial language for describing or expressing the instructions which
can be carried out by a digital
computer.
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In automatically sequenced computers, the instruction code is used when
describing or expressing sequences of instructions, and each instruction word
usually contains a part specifying the operation to be performed and one or
more addresses which identify a particular location in storage. Sometimes, an
address part of an instruction is not intended to specify a location in
storage but is used for some other purpose. If more than one address is used,
the code is called a multiple-address code. In a typical instruction of a
four-address code, the addresses specify the location of two operands, the
destination of the result, and the location of the next instruction in the
sequence. In a typical three-address code, the fourth address specifying the
location of the next instruction is dispensed with and the instructions are
taken from storage in a preassigned order. In a typical one-address or
single-address code, the address may specify either the location of an operand
to be taken from storage, the destination of a previously prepared result, or
the location of the next instruction. The arithmetic element usually contains
at least two storage locations, one of which is an accumulator. For example,
operations requiring two operands may obtain one operand from the main storage
and the other from a storage location in the arithmetic element which is
specified by the operation part.
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References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
