In computing, an instruction register (IR) is the part of a CPU's control unit that holds the instruction currently being executed or decoded. In simple processors each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and ultimately executed, which can take several steps.
Decoding the op-code in the instruction register includes determining the instruction, determining where its operands are in memory, retrieving the operands from memory, allocating processor resources to execute the command (in superscalar processors), etc.
The output of IR is available to control circuits which generate the timing signals that control the various processing elements involved in executing the instruction.
In the instruction cycle, the instruction is loaded into the Instruction register after the processor fetches it from the memory location pointed by the program counter.