.\" Copyright (c) 1986, 1991 Regents of the University of California.
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" @(#)mem.4 6.3 (Berkeley) 3/27/91
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
Only offsets within the bounds of
Kernel virtual memory is accessed through the interface
Only kernel virtual addresses that are currently mapped to memory are allowed.
allows access to the mapped portion of the
space. On the Tahoe the upper megabyte
of the physical address space is accessible through
this file (0xfff00000 through 0xffffffff).
Accesses to the upper 64 kilobytes of
16-bit address (the offset in this region) and a
.Dq No non-privileged short Tn I/O
Accesses to the remainder of the mapped region,
transfers with a 24-bit address
and a ``non-privileged standard''
modifier. This region is actually part of the region
between 0xfeff0000 and 0xffff0000
transfers with a 24-bit address.
Accesses to the remainder of the one gigabyte
generate transfers that utilize a 32-bit address with
a ``non-privileged extended'' address modifier. Any
32-bit address generated by a cpu access to this part
space have the upper two bits zero; thus,
for example, an access to physical address 0xfe000000
causes the address 0x3e000000 to be supplied in the
per-process data of the current process
is virtual address 0xbffff000.
.Bl -tag -width Pa -compact
Memory files are accessed one byte
at a time, an inappropiate method for some