GATE CS 1997 Q3.9 — Memory Management and Virtual Memory

Thrashing occurs when a virtual memory system spends a high percentage of its time swapping pages in and out of main memory (paging I/O) rather than executing actual instructions.

This situation typically arises when:

• The active pages required by the running processes (the sum of their working sets) exceed the available physical memory.
• As a result, a page fault occurs, requiring a page to be brought from disk. To make room, another active page is swapped out.
• This leads to a continuous cycle of page faults and disk operations, resulting in excessive page I/O and causing CPU utilization to drop drastically.

Let's analyze the options:

• Option A: Incorrect. Thrashing drastically increases page I/O.
• Option B: Incorrect. While the operating system may choose to decrease the degree of multiprogramming to resolve thrashing, thrashing itself is a state of excessive paging, not the act of decreasing multiprogramming.
• Option C: Correct. Thrashing directly implies excessive page I/O.
• Option D: Incorrect. Thrashing severely degrades system performance.