Question

Consider the virtual page reference string 1, 2, 3, 2, 4, 1, 3, 2, 4, 1 on a demand-paged virtual memory system running on a computer system with a main memory size of 3 page frames, which are initially empty. What will be the number of page faults under LRU, FIFO, and optimal page replacement policy?

Answer 1

The number of page faults for LRU and FIFO is 9, while the optimal page replacement policy results in fewer page faults, with a total of 6, given the page reference string and the main memory size of 3 page frames.

Step-by-step explanation:

The student's question pertains to page replacement algorithms in a computer's virtual memory system. Three algorithms are to be compared: LRU (Least Recently Used), FIFO (First In, First Out), and the optimal page replacement policy. To calculate the number of page faults for a given page reference string with a main memory size of 3 page frames, we must analyze the string and simulate each algorithm.

Let's break it down by algorithm:

1. LRU: Pages are replaced based on the least recently used policy. A page fault occurs when a page is not in the memory:

• Page fault count: 9

1. FIFO: Pages are replaced in the order they were brought into memory.

• Page fault count: 9

1. Optimal page replacement: This algorithm replaces the page that will not be used for the longest period of time.

• Page fault count: 6

All three algorithms begin with an empty memory, so the first three pages result in page faults immediately. Subsequent page faults occur when a new page must be brought into memory that isn't already present.