.\" 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) 1/28/88
.\"
.TH MEM 4 "January 28, 1988"
.UC 2
.SH NAME
mem, kmem \- main memory
.SH SYNOPSIS
.ft B
.nf
major device number(s):
	raw: 1
minor device encoding:
	mem: 0;  kmem: 1;  null: 2
.fi
.ft R
.SH DESCRIPTION
.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.
Examining and patching device registers is likely
to lead to unexpected results when read-only or write-only
bits are present.
.PP
On PDP-11s, the I/O page
begins at location 0160000 of
.I kmem
and the per-process data segment for the current process
begins at 0140000 and is USIZE clicks (64 bytes each) long.
.SH FILES
.ta \w'/dev/MAKEDEV.local  'u
/dev/mem
.br
/dev/kmem
.br
/dev/MAKEDEV	script to create special files
.br
/dev/MAKEDEV.local	script to localize special files
.DT
.SH BUGS
.PP
On PDP-11's, specifying an odd kernel or user address, or an odd transfer
count is [generally] slower than using all even parameters.
.PP
On machines with ENABLE/34(tm) memory mapping boards
the I/O page can be accessed only through \fIkmem\fP.