MEM(4)                                                                  MEM(4)



NAME
       mem, kmem - main memory

DESCRIPTION
       _M_e_m  is  a special file that is an image of the main memory of the com‐
       puter.  It may be used, for example, to examine (and even to patch) the
       system.

       Byte  addresses  in  _m_e_m  are interpreted as physical memory addresses.
       References to non-existent locations cause errors to be returned.

       The file _k_m_e_m is the same as _m_e_m  except  that  kernel  virtual  memory
       rather than physical memory is accessed.  Only kernel virtual addresses
       that are mapped to memory are allowed.  The file _k_U_m_e_m also  refers  to
       kernel virtual memory, but may be used to access areas mapped to UNIBUS
       address space and other I/O areas.  It forces all accesses to use  word
       (short  integer)  accesses.  Examining and patching device registers is
       likely to lead to unexpected results when read-only or write-only  bits
       are present.

       On VAX 11/780 the I/O space begins at physical address 20000000(16); on
       an 11/750 I/O space addresses are  of  the  form  fxxxxx(16).   On  all
       VAX’en  per-process  data  for  the current process is UPAGES long, and
       ends at virtual address 80000000(16).

FILES
       /dev/mem
       /dev/kmem
       /dev/kUmem



4th Berkeley Distribution        May 16, 1986                           MEM(4)