The Free On-line Dictionary of Computing (30 December 2018):
instruction register
(IR) The part of a central processing unit
(CPU) control unit that holds the machine instruction
currently being executed. The CPU's fetch-execute cycle
loads instructions from memory into the instruction
register. The IR in turn drives the instruction decoding
logic that determines what operation teh CPU should perform on
what data.
Modern processors have an instruction pipeline to minimise
the time the control unit is waiting for instructions and data
to be fetched from memory. This may distrubute the job of the
IR over several registers in the pipeline.
(2018-08-31)