MEM(4)		    UNIX Programmer's Manual		   MEM(4)



NAME
     mem, kmem - main memory

SYNOPSIS
     major device number(s):
	  raw: 1
     minor device encoding:
	  mem: 0;  kmem: 1;  null: 2

DESCRIPTION
     _M_e_m is a special file that is an image of the main memory of
     the computer.  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.
     Examining and patching device registers is likely to lead to
     unexpected results when read-only or write-only bits are
     present.

     On PDP-11s, the I/O page begins at location 0160000 of _k_m_e_m
     and the per-process data segment for the current process
     begins at 0140000 and is USIZE clicks (64 bytes each) long.

FILES
     /dev/mem
     /dev/kmem
     /dev/MAKEDEV	 script to create special files
     /dev/MAKEDEV.local  script to localize special files

BUGS
     On PDP-11's, specifying an odd kernel or user address, or an
     odd transfer count is [generally] slower than using all even
     parameters.

     On machines with ENABLE/34(tm) memory mapping boards the I/O
     page can be accessed only through _k_m_e_m.













Printed 11/26/99	January 28, 1988			1