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INTRODUCTION TO THE INTEL ARCHITECTURE
2.5.5.Retirement Unit
The retirement unit commits the results of speculatively executed micro-ops to permanent
machine state and removes the micro-ops from the reorder buffer. Like the reservation station,
the retirement unit continuously checks the status of micro-ops in the reorder buffer, looking for
ones that have been executed and no longer have any dependencies with other micro-ops in the
instruction pool. It then retires completed micro-ops in their original program order, taking into
accounts interrupts, exceptions, breakpoints, and branch mispredictions.
The retirement unit can retire three micro-ops per clock. In retiring a micro-op, it writes the
results to the retirement register file and/or memory. The retirement register file contains the IA
registers (eight general-purpose registers and eight floating-point data registers). After the
results have been committed to machine state, the micro-op is removed from the reorder buffer.
