mem(7)                           DG/UX R4.11                          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).


Licensed material--property of copyright holder(s)