What is virtual memory and how does paging work?

• A. Virtual memory is a direct mapping of virtual addresses to physical addresses with no translation; paging is not involved.
• B. Virtual memory provides an address space abstraction; paging divides memory into fixed-size pages with a page table mapping virtual pages to physical frames.
• C. Paging loads the entire program into RAM before execution.
• D. Virtual memory uses segmentation exclusively instead of paging.

Answer: (B)

Virtual memory provides an address space abstraction that lets each process feel as if it has its own large, contiguous block of memory, separate from other processes and from the physical RAM. To make that possible, memory is managed in fixed-size chunks called pages, while the actual physical memory is divided into frames of the same size. A page table stores the mapping from each virtual page to a physical frame, and the memory management unit translates a process’s virtual addresses to real physical addresses as the program runs. In practice, a fast cache called the translation lookaside buffer helps speed up these translations.

If the page needed by the program isn’t currently in RAM, the system triggers a page fault, and the operating system must bring that page in from disk (and possibly evict another page) before the process can continue. This mechanism lets the system use more memory than is physically installed and provides isolation and protection between processes.

The other ideas don’t fit because virtual memory relies on translating virtual addresses to physical addresses rather than a direct, one-to-one mapping. It’s not required to load the entire program into RAM before execution, and many systems use paging (often alongside other techniques like segmentation), not segmentation exclusively.