Follow Us :

Aug2016 cs Q51

0. An operating system supports a paged virtual memory, using a central processor with a cycle time of one microsecond. It costs an additional one microsecond to access a page other than the current one. Pages have 1000 words, and the paging device is a drum that rotates at 3000 revolutions per minute and transfers one million words per second. Further, one percent of all instructions executed accessed a page other than the current page. The instruction that accessed another page, 80% accessed a page already in memory and when a new page was required, the replaced page was modified 50% of the time. What is the effective access time on this system, assuming that the system is running only one process and the processor is idle during drum transfers?

  • Option : B
  • Explanation :
    Effective access time = 0.99 * (1 µs) + 0.8 *.02 µs + 0.001 * ( 10000 µs + 1000 µs) + 0.001 * (20000 µs + 2000 µs) = (0.99 +0.016+22.0+11.0) µs = 34 µs So, option (B) is correct.
Cancel reply
Cancel reply