Virtual Memory
A memory-management mechanism that gives processes a virtual address space and maps virtual addresses to physical memory through page tables.
Virtual memory separates the address space seen by a process from the physical layout of RAM. A CPU-generated virtual address is translated through the MMU and page tables; the TLB caches frequently used translations. A missing or not-yet-materialized mapping can trigger a page fault.
It should not be reduced to "using disk when RAM is full." Process isolation, shared memory, memory-mapped files, copy-on-write, and demand paging all rely on the same address-translation machinery. Performance diagnosis therefore needs to consider resident memory, fault rates, and TLB behavior together.
Related: Page Fault, TLB, Memory-Mapped I/O, Copy-on-Write, Operating Systems: Processes, Memory, Files and I/O.