.\"	$OpenBSD: mem.4,v 1.3 2000/04/27 00:35:56 deraadt Exp $
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.\"     from: @(#)mem.4	5.2 (Berkeley) 3/27/91
.\"
.Dd March 27, 1991
.Dt MEM 4 hp300
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd main memory
.Sh DESCRIPTION
The file
.Nm /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.
An error will be returned if an attempt is made to reference
an offset outside of
.Nm /dev/mem .
.Pp
Kernel virtual memory is accessed via the file
.Nm /dev/kmem
in the same manner as
.Nm /dev/mem .
Only kernel virtual addresses that are currently mapped to memory are allowed.
.Sh HP300
On the
.Tn HP300 ,
the last byte of physical memory is always
.Li 0xFFFFFFFF .
Therefore, on an
.Tn HP300
with
8Mb of memory, physical memory would start
at
.Li 0xFF800000 .
On the
.Tn HP300 ,
kernel virtual memory runs from
.Li 0
to about
.Li 0x2400000 .
.Pp
Writeability of these devices is controlled by the system
.Xr securelevel 7 .
.Sh FILES
.Bl -tag -width /dev/kmem -compact
.It Pa /dev/mem
.It Pa /dev/kmem
.El
.Sh SEE ALSO
.Xr securelevel 7
.Sh HISTORY
The files
.Nm mem
and
.Nm kmem
appeared in
.At v6 .