.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)mem.4	6.2 (Berkeley) 5/16/86
.\"
.TH MEM 4 "May 16, 1986"
.UC 4
.SH NAME
mem, kmem \- main memory
.SH DESCRIPTION
.lg
.I Mem
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.
.PP
Byte addresses in
.I mem
are interpreted as physical memory addresses.
References to non-existent locations cause errors to be returned.
.PP
The file
.I kmem
is the same as 
.I mem
except that kernel virtual memory
rather than physical memory is accessed.
Only kernel virtual addresses that are mapped to memory are allowed.
The file
.I kUmem
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.
.PP
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).
.SH FILES
/dev/mem
.br
/dev/kmem
.br
/dev/kUmem