What is a disadvantage of virtual memory?

• A. It speeds up CPU by moving data into RAM
• B. If the CPU needs to read data stored in virtual memory, it needs to be moved into RAM which has a slower transfer rate and makes the computer slow to respond
• C. It automatically caches all files
• D. It makes the computer start faster

Answer: (B)

The main point is that virtual memory can slow a system when data isn’t already in RAM. It uses disk space as an extension of RAM, but when the CPU needs data that isn’t resident in RAM, the operating system must fetch that page from disk into RAM. Disk access is much slower than RAM access, so each such page fault introduces notable latency and can stall the CPU. If many pages must be swapped in and out, performance can degrade further, a situation often called thrashing. So the drawback of virtual memory is this potential for slow response due to moving data from disk into memory. The other ideas—that virtual memory speeds up the CPU, caches all files automatically, or makes the system boot faster—don’t reflect this cost.