Consider the following justifications for commonly using the two-level CPU…
2014
Consider the following justifications for commonly using the two-level CPU scheduling :
I. It is used when memory is too small to hold all the ready processes.
II. Because its performance is same as that of the FIFO.
III. Because it facilitates putting some set of processes into memory and a choice is made from that.
IV. Because it does not allow to adjust the set of in-core processes.
Which of the following is true ?
- A.
I, III and IV
- B.
I and II
- C.
III and IV
- D.
I and III
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Correct answer: D
Answer: I and III
Explanation:
Statement I is true: Two-level scheduling is used when main memory is too small to hold all ready processes. The outer level decides which processes are kept in memory, and the inner level schedules among those in-core processes.
Statement II is false: Two-level scheduling is not equivalent in performance to FIFO. It adds management overhead to control which processes are resident, and its benefits are in better utilization when memory is limited, not in matching FIFO performance.
Statement III is true: The scheme facilitates loading a chosen set of processes into memory and making scheduling decisions from that set.
Statement IV is false: Two-level scheduling explicitly allows adjusting which processes are in-core (for example by swapping processes in and out), so it does allow changing the in-core set.
Therefore the correct combination of true statements is I and III.