Virtual Memory Concept
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Virtual Memory concept • Solves problem of limited memory space – Creates illusion of more memory than exists • Creates 2 types of addresses – Virtual addresses • Referenced by processes – Physical addresses • Describes locations in main memory • Memory management unit (MMU) – Dynamic address translation – Translates virtual addresses to physical address Virtual Memory: Basic Concepts • Virtual address space, V – Range of virtual addresses that a process may reference • Real address space, R – Range of physical addresses available on a particular computer system • Dynamic address translation (DAT) mechanism – Converts virtual addresses to physical addresses during program execution • |V| is often much greater than |R| – OS must store parts of V for each process outside of main memory • Two-level storage – OS shuttles portions of V between main memory (and caches) and secondary storage
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A virtual memory file
Transcript of Virtual Memory Concept
Virtual Memory concept Solves problem of limited memory space Creates illusion of more memory than exists Creates 2 types of addresses Virtual addresses Referenced by processes Physical addresses Describes locations in main memory Memory management unit (MMU) Dynamic address translation Translates virtual addresses to physical addressVirtual Memory: Basic Concepts Virtual address space, V Range of virtual addresses that a process may reference Real address space, R Range of physical addresses available on a particular computer system Dynamic address translation (DAT) mechanism Converts virtual addresses to physical addresses during program execution |V| is often much greater than |R| OS must store parts of V for each process outside of main memory Two-level storage OS shuttles portions of V between main memory (and caches) and secondary storage
Two-level Storage backing store: maintained on hard drive contains complete virtual memory real memory: portion of virtual memory that is currently in use Process can only access real memory Management of mapping is essential
