Which of the following describes demand paging?

• A. Demand paging loads the entire program into memory before execution.
• B. Demand paging loads pages on first access.
• C. Demand paging prevents paging.
• D. Demand paging requires all pages be in memory.

Answer: (B)

Demand paging loads pages on first access. It keeps a program’s pages on disk and only brings a page into physical memory when the program actually tries to use it. When such a reference occurs, the system detects a page fault, fetches the needed page from disk into memory, and then resumes execution. This lets large programs run with less RAM because only the actively used pages occupy memory.

The other descriptions describe loading everything up front, which is eager loading, or removing paging entirely, which defeats the purpose of demand paging, or requiring all pages to be in memory, which also contradicts the on-demand approach.