catflap.org Online Dictionary Query

  virtual memory
       
           A system allowing a computer program to
          behave as though the computer's memory was larger than the
          actual physical RAM.  The excess is stored on hard disk
          and copied to RAM as required.
       
          Virtual memory is usually much larger than physical memory,
          making it possible to run programs for which the total code
          plus data size is greater than the amount of RAM available.
          This is known as "{demand paged virtual memory".  A page is
          copied from disk to RAM ("paged in") when an attempt is made
          to access it and it is not already present.  This paging is
          performed automatically by collaboration between the CPU,
          the memory management unit (MMU), and the operating system
          kernel.  The program is unaware of virtual memory, it just
          sees a large address space, only part of which corresponds
          to physical memory at any instant.
       
          The virtual address space is divided into pages.  Each
          virtual address output by the CPU is split into a
          (virtual) page number (the most significant bits) and an
          offset within the page (the N least significant bits).  Each
          page thus contains 2^N bytes (or whatever the unit of
          addressing is).  The offset is left unchanged and the memory
          management unit (MMU) maps the virtual page number to a
          physical page number.  This is recombined with the offset to
          give a physical address - a location in physical memory
          ({RAM).
       
          The performance of a program will depend dramatically on how
          its memory access pattern interacts with the paging scheme.
          If accesses exhibit a lot of locality of reference,
          i.e. each access tends to be close to previous accesses, the
          performance will be better than if accesses are randomly
          distributed over the program's address space thus requiring
          more paging.
       
          In a multitasking system, physical memory may contain pages
          belonging to several programs.  Without demand paging, an OS
          would need to allocate physical memory for the whole of every
          active program and its data.  Such a system might still use an
          MMU so that each program could be located at the same
          virtual address and not require run-time relocation.  Thus
          virtual addressing does not necessarily imply the existence of
          virtual memory.  Similarly, a multitasking system might load
          the whole program and its data into physical memory when it is
          to be executed and copy it all out to disk when its
          timeslice expired.  Such "swapping" does not imply virtual
          memory and is less efficient than paging.
       
          Some application programs implement virtual memory wholly in
          software, by translating every virtual memory access into a
          file access, but efficient virtual memory requires hardware
          and operating system support.
       
          (2002-11-26)
       
       

  virtual memory
       n : (computer science) memory created by using the hard disk to
           simulate additional random-access memory; the addressable
           storage space available to the user of a computer system
           in which virtual addresses are mapped into real addresses
           [syn: virtual storage]

  virtual memory
     n.
     (lb en computing) Memory that appears to be RAM but is being
  simulated (by a process called paging) on a hard disk; allows a computer
  to operate as if it had more memory than it actually does, but with some
  loss of performance

  virtual memory
     n.
     (lb en computing) Memory that appears to be RAM but is being
  simulated (by a process called paging) on a hard disk; allows a computer
  to operate as if it had more memory than it actually does, but with some
  loss of performance

  virtual memory
     n.
     (lb en computing) Memory that appears to be RAM but is being
  simulated (by a process called paging) on a hard disk; allows a computer
  to operate as if it had more memory than it actually does, but with some
  loss of performance

  virtual memory
     n.
     (lb en computing) Memory that appears to be RAM but is being
  simulated (by a process called paging) on a hard disk; allows a computer
  to operate as if it had more memory than it actually does, but with some
  loss of performance

  virtual memory /vˈɜːtʃuːəl mˈɛməɹi/
  virtueller Speicher, virtueller Arbeitsspeicher
   see: memory, storage, store, active storage, dynamic storage, erasable storage, retentive memory, serial memory, serial store, bootstrap memory
  

  virtual memory /vˈɜːtʃuːəl mˈɛməɹi/ 
  virtuaalimuisti
  memory that appears to be RAM but is being simulated

  virtual memory /vˈɜːtʃuːəl mˈɛməɹi/
  prividna memorija, virtualna memorija

     虚拟内存