Homework Assignment 9

Homework Assignment 9

• Silberschatz et al, Operating System Concepts, 9th edition, Chapter 9, Virtual Memory
  1. A certain computer provides its users with a virtual-memory space of 2⁴⁸ bytes. The computer has 2²⁰ bytes of physical memory. The virtual memory is implemented by paging, and the page size is 2048 bytes. A user process generates the virtual address 12312312. Explain how the system establishes the corresponding physical location. Distinguish between software and hardware operations.

  2. Assume we have a demand-paged memory. The page table is held in registers. It takes 9 milliseconds to service a page fault if an empty page is available or the replaced page is not modified, and 21 milliseconds if the replaced page is modified. Memory access time is 100 nanoseconds. Assume that the page to be replaced is modified 60 percent of the time. What is the maximum acceptable page-fault rate for an effective access time of no more than 200 nanoseconds?

  3. Discuss situations under which the least frequently used page-replacement algorithm generates fewer page faults than the FIFO page replacement algorithm. Also discuss under what circumstance the opposite holds.

  4. Consider a demand-paging system with the following time-measured utilizations:
     • CPU utilization 20%
     • Paging disk 97.7%
     • Other I/O devices 5%

     For each of the following, say whether it will (or is likely to) improve CPU utilization. Explain your answers.

     1. Install a faster CPU.
     2. Install a bigger paging disk.
     3. Increase the degree of multiprogramming.
     4. Decrease the degree of multiprogramming.
     5. Install more main memory.
     6. Install a faster hard disk or multiple controllers with multiple hard disks.
     7. Add prepaging to the page fetch algorithms.
     8. Increase the page size.