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 6.1 (Berkeley) 05/15/85

C 4 mem, kmem - main memory .lg 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.

Byte addresses in mem are interpreted as physical memory addresses. References to non-existent locations cause errors to be returned.

Examining and patching device registers is likely to lead to unexpected results when read-only or write-only bits are present.

The file kmem is the same as mem except that kernel virtual memory rather than physical memory is accessed.

On PDP11's, the I/O page begins at location 0160000 of kmem and per-process data for the current process begins at 0140000. 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 at virtual 7ffff000(16).

/dev/mem

/dev/kmem

On PDP11's and VAX's, memory files are accessed one byte at a time, an inappropriate method for some device registers.