.\"	$OpenBSD: mem.4,v 1.9 2003/06/06 10:29:42 jmc Exp $
.\"	$NetBSD: mem.4,v 1.3 1996/03/03 17:13:50 thorpej Exp $
.\"
.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    notice, this list of conditions and the following disclaimer.
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
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.\"
.\"     from: @(#)mem.4	6.3 (Berkeley) 3/27/91
.\"
.Dd March 27, 1991
.Dt MEM 4 vax
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd memory files
.Sh DESCRIPTION
The special file
.Pa /dev/mem
is an interface to the physical memory of the computer.
Byte offsets in this file are interpreted as physical memory addresses.
Reading and writing this file is equivalent to reading and writing
memory itself.
Only offsets within the bounds of
.Pa /dev/mem
are allowed.
.Pp
Kernel virtual memory is accessed through the interface
.Pa /dev/kmem
in the same manner as
.Pa /dev/mem .
Only kernel virtual addresses that are currently mapped to memory are allowed.
.Pp
On the
.Tn VAX
11/780 (and others),
the
.Tn I/O
space base address is
20000000(16);
on an 11/750
the
.Tn I/O
space addresses are of the form fxxxxx(16).
On all
.Tn VAX Ns 'en
the
per-process data
size
for the current process
is
.Dv UPAGES
long and ends at the virtual address 80000000(16).
.Pp
Writeability of these devices is controlled by the system
.Xr securelevel 7 .
.Sh FILES
.Bl -tag -width Pa -compact
.It /dev/mem
.It /dev/kmem
.El
.Sh SEE ALSO
.Xr securelevel 7
.Sh HISTORY
The
.Pa /dev/mem
and
.Pa /dev/kmem
files appeared in
.At v6 .