Need for 4 stages

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

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

• Dispatch and Issue

  • Check for structural hazards (reservation stations busy, reorder buffer full). If one exists, stall the instruction and those following
  • If dispatch possible, send values to reservation station if the values 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
  • When both operands are ready, issue to functional unit

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