Virtual memory

Virtual memory maps a program’s virtual addresses to physical memory and, when needed, storage. It gives each process a private address space that can exceed available RAM.

Virtual address space: The range of virtual addresses a process can use, organized independently of physical memory. It is the per-process address range that virtual memory presents to programs.
Paging: A memory-management scheme that divides address spaces into fixed-size pages and physical memory into frames. Virtual memory commonly uses paging to map equal-sized units between addresses and RAM.
Process isolation: The separation of processes so one process cannot freely access another’s memory or resources. Separate virtual address spaces are a primary way operating systems isolate processes.
Physical address: An address that identifies a location in a computer’s physical memory. Virtual addresses require translation; physical addresses identify the resulting RAM locations.
Page table: A data structure that records mappings from virtual pages to physical frames or other backing locations. It stores the mappings used to translate a process’s virtual addresses.
Memory page: A fixed-size block of virtual address space used as a unit of mapping and memory management. Pages are the virtual units that page tables map to physical frames.
Shared library: A library whose code can be loaded into and used by multiple programs at runtime. Operating systems can map the same read-only library pages into many processes.
Overlay (programming): A programming technique that reuses a fixed memory region for different program modules loaded at different times. Overlays manage limited memory explicitly, rather than presenting a broad mapped address space.
Memory management unit: A processor component that performs address translation and enforces memory-access permissions. It consults translation data as programs access virtual addresses.
Page frame: A fixed-size block of physical memory capable of holding one memory page. Frames provide the RAM destinations for mapped virtual pages.

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