Question

2. Consider the same computer system used in problem 1. The following trace of accessed page numbers was recorded over time: 1, 0, 2, 2, 1, 7, 6, 7, 0, 1, 2, 0, 3, 0, 4, 5, 1, 5, 2, 4, 5, 6, 7, 6, 7, 2, 4, 2, 7, 3, 3, 2, 3. The first two page references were reads, while the third was a write, and every third reference after that was also a write operation.

c) Assuming that the clock replacement policy is used in combination with a modify bit for write operations, show how the contents of the four memory frames change over the sequence of page references. Compute the hit rate assuming that all frames are initially empty

Answer 1

• In a operating systems that use paging for memory management, page replacement algorithm are needed to decide which page needed to be replaced and when new page come in.
• whenever a new page is referred and not present in memory, page fault occurs and the operating system replaces one of the existing pages with newly needed page
• Page fault is a type of interrupt, raised by the hardware when a running program accesses a memory page that is mapped into the virtual address space but not loaded in physical memory
• According to question

Hit ratio = 16/33

1 0 2 2 1 7 6 7 0 1 2 0 3 0 4 5 1 5 2 4 5 6 7 6 7 2 4 2 7 3 3 2 3

PF1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4 4 4 4 4 4 4 4 4 4 4 2 2 2 2 2 2 2 2

PF2 - 0 0 0 0 0 6 6 6 6 2 2 2 2 2 5 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4

PF3 - - 2 2 2 2 2 2 0 0 0 0 0 0 0 0 0 0 2 2 2 2 7 7 7 7 7 7 7 7 7 7 7

PF4 - - - - - 7 7 7 7 7 7 7 3 3 3 3 1 1 1 1 1 6 6 6 6 6 6 6 6 3 3 3 3

F F F F F F F F F F F F F F F F F