redhat man page for port

MEM(4)							     Linux Programmer's Manual							    MEM(4)

NAME
       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:mem /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:mem /dev/kmem

       Port is similar to mem, but the IO 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

SEE ALSO
       chown(1), mknod(1), ioperm(2)

Linux								    1992-11-21								    MEM(4)