An instruction goes through 4 stages

• In Tomasulo’s solution 3 stages: issue, execute, write

• Now 4 stages: issue, execute, write, commit

• Issue (often call dispatch)

  • Check for structural hazards (reservation stations busy, reorder buffer full). If one exists, stall the instruction and those following
  • If issue possible, send values to reservation station if they are available in either the registers or the reorder buffer. Otherwise send tag.
  • Allocate an entry in the reorder buffer and send its number to the reservation station

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