Quetion 6 : Consider the "in-order-issue/in-order-completion" execution sequence shown in f In Figure Decode OWE Execute 12 12 12 14 16 13 16 13 15 15 16 Write 024/06/02 11 3 4 11 12 13 13 N 15 16 a. Identify the most likely reason why I could not enter the execute fourth cycle. stage until the [2] b. Will "in-order issue/out-of-order completion" or "out-of-order issue/out-of-order completion" fix this? If so, which? Explain

Answer: 

a. Identify the most likely reason why I could not enter the execute stage until the fourth cycle.

One likely reason an instruction couldn't enter the execute stage until the fourth cycle is due to data hazards or resource conflicts:

1. Data Hazards: If the instruction depends on the result of a previous instruction that hasn't completed yet, it cannot proceed to the execute stage. This is often referred to as a Read After Write (RAW) hazard.

2. Resource Conflicts: If the required functional unit for execution (e.g., an ALU) is occupied by another instruction, the instruction will have to wait until the resource becomes available.

b. Will "in-order issue/out-of-order completion" or "out-of-order issue/out-of-order completion" fix this? If so, which? Explain

In-order issue/out-of-order completion might help if the problem is related to instructions that can complete earlier being delayed by instructions that take longer to execute. This allows the processor to finish instructions as soon as their execution is complete, rather than waiting for previous instructions that are still executing. However, this does not solve the problem if the issue is related to dependencies that must be resolved before execution can begin.

Out-of-order issue/out-of-order completion can significantly help with both data hazards and resource conflicts. This allows the processor to issue and execute instructions as soon as their dependencies are resolved, regardless of their original order. Instructions can bypass other instructions that are waiting for resources or data dependencies, improving overall execution efficiency and reducing stalls.

Therefore, out-of-order issue/out-of-order completion would be the more effective solution in this scenario, as it addresses both potential data hazards and resource conflicts by allowing more flexible instruction scheduling.