UNIVERSITY OF WISCONSIN-MADISON
Computer Sciences Department
CS 537
Fall 1997 		A. Arpaci-Dusseau
Sample Quiz: Virtual Memory

Paging to Disk

Consider computer whose operating systems is using demand paging. We measure the various resource utilizations under a particular workload and see:
CPU utilization: 20% of the time
Paging disk utilization: 99% of the time

Which of these (if any) should improve the CPU utilization in these circumstances? Why or why not?

  1. Get a faster CPU.

    This system appears to be limited by the speed of the paging disk. So, a faster CPU would only decrease CPU utilization.

  2. Get a bigger disk.

    The size of the disk would allow large virtual address spaces or allow more processes to run, but would not increase CPU utilization. It might actually decrease it, if disk head seek time was increased.

  3. Get a faster disk.

    A faster disk would allow paging requests to be handled faster and would probably increase CPU utilization.

  4. Increase the degree of multiprogramming.

    Increasing multiprogramming might increase the utilization, if the jobs did not do much paging. Most likely, it would just add to the disk queue, further slowing the system (decreasing CPU utilization).

  5. Decrease the degree of multiprogramming.

    Decreasing the multiprogramming level would likely increase CPU utilization if the system was thrashing because too many jobs were competing for the page frames.