What is thrashing in virtual memory systems ?

Thrashing occurs when a system spends more time handling page faults than executing useful instructions. This happens when the degree of multiprogramming is too high, causing the working set of processes to exceed available physical memory. As a result, pages are constantly swapped in and out of RAM, leading to excessive page faults. This creates a cycle where the CPU is idle while waiting for I/O operations to complete, significantly degrading system performance. While excessive disk I/O (Option A) is a symptom of thrashing, the root cause and defining characteristic are the excessive page faults themselves. CPU overutilization (Option C) is incorrect because thrashing actually leads to low effective CPU utilization due to waiting times. Memory fragmentation (Option D) is a separate issue related to memory allocation inefficiencies, not the constant paging activity that defines thrashing. Therefore, excessive page faults accurately describe this critical performance bottleneck.