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3 definitions found
 for MMU
From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :

  MMU
         Mass Memory Unit
         

From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :

  MMU
         Memory Management Unit
         

From The Free On-line Dictionary of Computing (30 December 2018) :

  Memory Management Unit
  MMU
  Paged Memory Management Unit
  
      (MMU, "Paged Memory Management
     Unit", PMMU) A hardware device or circuit that supports
     virtual memory and paging by translating virtual
     addresses into physical addresses.
  
     The virtual address space (the range of addresses used by
     the processor) is divided into pages, whose size is 2^N,
     usually a few kilobytes.  The bottom N bits of the address
     (the offset within a page) are left unchanged.  The upper
     address bits are the (virtual) page number.  The MMU
     contains a page table which is indexed (possibly
     associatively) by the page number.  Each page table entry
     (PTE) gives the physical page number corresponding to the
     virtual one.  This is combined with the page offset to give
     the complete physical address.
  
     A PTE may also include information about whether the page has
     been written to, when it was last used (for a least recently
     used replacement algorithm), what kind of processes ({user
     mode, supervisor mode) may read and write it, and whether
     it should be cached.
  
     It is possible that no physical memory ({RAM) has been
     allocated to a given virtual page, in which case the MMU will
     signal a "{page fault" to the CPU.  The operating system
     will then try to find a spare page of RAM and set up a new PTE
     to map it to the requested virtual address.  If no RAM is free
     it may be necessary to choose an existing page, using some
     replacement algorithm, and save it to disk (this is known as
     "{paging").  There may also be a shortage of PTEs, in which
     case the OS will have to free one for the new mapping.
  
     In a multitasking system all processes compete for the use
     of memory and of the MMU.  Some memory management
     architectures allow each process to have its own area or
     configuration of the page table, with a mechanism to switch
     between different mappings on a process switch.  This means
     that all processes can have the same virtual address space
     rather than require load-time relocation.
  
     An MMU also solves the problem of fragmentation of memory.
     After blocks of memory have been allocated and freed, the free
     memory may become fragmented (discontinuous) so that the
     largest contiguous block of free memory may be much smaller
     than the total amount.  With virtual memory, a contiguous
     range of virtual addresses can be mapped to several
     non-contiguous blocks of physical memory.
  
     In early designs memory management was performed by a separate
     integrated circuit such as the MC 68851 used with the
     Motorola 68020 CPU in the Macintosh II or the Z8015
     used with the Zilog Z80 family of processors.  Later CPUs
     such as the Motorola 68030 and the ZILOG Z280 have MMUs on
     the same IC as the CPU.
  
     (1999-05-24)
  

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