For the following page reference string 4, 3, 2, 1, 4, 5, 4, 3, 2, 1, 5 the number of page faults that occur in Least Recently Used (LRU) page replacement algorithm with frame size 3 is:

Correct option is C

Given:
1. Page Reference String: 4, 3, 2, 1, 4, 5, 4, 3, 2, 1, 5
2. Frame Size: 3
3. Algorithm: Least Recently Used (LRU)
We need to calculate the number of page faults.
Step 1: Understanding LRU Algorithm
· The LRU page replacement algorithm replaces the page that has not been used for the longest time in memory.
· Initially, the memory frames are empty.
· As pages are referenced:
· If the page is not in memory, a page fault occurs.
· If the memory is full, the least recently used page is replaced.
Step 2: Simulate the Page Reference String Initial Memory State: Empty

Step 3: Count Page Faults
Total Page Faults: 10
Information Booster
1. LRU Characteristics:
· Tracks usage history of pages to identify the least recently used page.
· Requires additional data structures like stacks or counters for implementation.
2. Page Replacement Algorithms:
· FIFO (First-In-First-Out): Replaces the oldest page.
· Optimal: Replaces the page that will not be used for the longest period in the future.
· LRU: Replaces the page least recently used.
Additional Knowledge
· Page Faults: Occur when a required page is not present in memory.
· Frame Size Impact: Larger frame sizes generally reduce page faults but increase memory usage.
· Real-World Usage: LRU is commonly used in operating systems for efficient memory management.