A Level Computer Science OCR Practice Exam

What is meant by "flushing the pipe" in a pipelining context?

1. Clearing the CPU to handle the next instruction

2. Removing unnecessary data from memory

3. Interrupting the current process

4. Exiting the program safely

The correct answer is: Clearing the CPU to handle the next instruction

In the context of pipelining, "flushing the pipe" refers to the process of clearing out the instructions that are currently being processed in the pipeline. This occurs typically when an interrupt service routine is activated or when a branch instruction alters the flow of execution. By clearing the pipeline (or "flushing"), the system ensures that it only processes the correct instructions that follow the point of the deviation in control flow. When the pipeline is flushed, any instructions that were partially processed (but are no longer valid due to the change in program flow) are discarded. This allows the CPU to reset its execution path and start processing the new set of instructions that adhere to the updated control flow. Therefore, the option discussing clearing the CPU to handle the next instruction accurately conveys the essential aspect of flushing: it allows the processor to maintain correctness and efficiency in managing the instruction execution sequence.