3BSD/usr/man/man4/mem.4

.TH MEM 4 
.SH NAME
mem, kmem \- main memory
.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
Examining and patching device registers is likely
to lead to unexpected results when read-only or write-only
bits are present.
.PP
The file
.I kmem
is the same as 
.I mem
except that kernel virtual memory
rather than physical memory is accessed.
.PP
On PDP11's, the I/O page
begins at location 0160000 of
.I kmem
and per-process data for the current process
begins at 0140000.
On VAX11's the I/O space begins at physical address 20000000(16)
and per-process data for the current process is at virtual 80020000(16).
.SH FILES
/dev/mem,
/dev/kmem
.SH BUGS
On PDP11's and VAX11's, memory files are accessed one byte
at a time, an inapproriate method for some
device registers.