What is a key benefit of virtual memory with demand paging?

• A. The system preloads all pages at program start.
• B. Virtual memory prohibits more address space than physical RAM.
• C. Demand paging uses speculative prefetching of pages.
• D. Virtual memory allows processes to address more memory than physically installed, and demand paging loads pages on first access.

Answer: (D)

Demand paging with virtual memory hinges on two ideas: a process can address more memory than physically installed, and pages are brought into RAM only when they are actually accessed. This on-demand loading means the system keeps most of the program’s data and code on a disk-backed backing store and fetches pages into memory as needed, which lets large programs run even on limited RAM and keeps memory usage efficient.

That’s why the statement describing both aspects—addressing more memory than RAM and loading pages on first access—best captures the benefit. Preloading all pages at program start would defeat the purpose of demand paging by loading everything up front. Virtual memory does not prohibit more address space; it enables it by mapping to disk. Speculative prefetching is not the defining feature of demand paging, which centers on loading pages the first time they’re actually referenced.