mem(7)                     DG/UX 4.30                      mem(7)



     NAME
          mem - main system memory

     DESCRIPTION
          Mem is a character special pseudo-device that provides
          access to the system's physical main memory for direct
          reading and writing.  The file pointer is treated as a
          physical byte address within main memory.

          For the open and close system calls, user visible
          functionality is the same as for an ordinary disk file.

          For the read system call, the contents of physical main
          memory at the address contained in the file pointer are
          transferred into the caller's buffer.  If any part of the
          requested data would be past the end of physical memory, no
          data is transferred and the error ENXIO is returned.  No
          consistency guarantees are made; the physical memory being
          read may change while the read is in progress.

          For the write system call, the contents of caller's buffer
          are transferred into physical main memory at the address
          contained in the file pointer.  If the write call would
          attempt to transfer data to locations past the end of
          physical main memory, no data will be transferred and the
          error ENXIO will be returned.  Correct operation of the
          system is not guaranteed after physical memory has been
          modified with this call.

          There are no ioctl system calls specific to the character
          special device mem. Other ioctl calls that apply to ordinary
          disk files also apply to mem.

          Select always returns READY for both read and write
          operations.

     FILES
          /dev/mem

     SEE ALSO
          kmem(7)














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