From Linux Man Pages
mem, kmem, port - system memory, kernel memory and system ports
DESCRIPTION
mem is a character device file that is an image of the main memory of the computer. It may be used, for example,
to examine (and even 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 is likely to lead to unexpected results when read-only or write-only bits are present.
It is typically created by:
mknod -m 660 /dev/mem c 1 1
chown root:kmem /dev/mem
The file kmem is the same as mem, except that the kernel virtual memory rather than physical memory is accessed.
It is typically created by:
mknod -m 640 /dev/kmem c 1 2
chown root:kmem /dev/kmem
port is similar to mem, but the I/O ports are accessed.
It is typically created by:
mknod -m 660 /dev/port c 1 4
chown root:mem /dev/port
FILES
/dev/mem
/dev/kmem
/dev/port
RELATED
chown(1), mknod(1), ioperm(2)
CATEGORY