Execution steps under scoreboard control
2. Dispatch (Read operands)
- When the instruction is issued, the execution unit is reserved (becomes busy)
- Operands are read in the execution unit when they are both ready (i.e., are not results of still executing instructions). This prevents RAW hazards (this conservative approach was taken because the CDC 6600 was not pipelined)
3. Execution
- One or more cycles depending on functional unit latency
- When execution completes, the unit notifies the scoreboard it’s ready to write the result