The file /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 /dev/mem
.
Kernel virtual memory is accessed via the file
/dev/kmem
in the same manner as
/dev/mem
. Only kernel virtual addresses that are
currently mapped to memory are allowed.
On the HP300, the last byte of physical memory is always
0xFFFFFFFF
. Therefore, on an HP300 with 8MB of memory,
physical memory would start at 0xFF800000
. On the
HP300, kernel virtual memory runs from 0
to about
0x2400000
.
The files mem
and kmem
appeared
in Version 6 AT&T UNIX.