| MEM(4) | Device Drivers Manual (mac68k) | MEM(4) | 
mem, kmem —
/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 Macintosh, physical memory may be discontiguous; kernel virtual memory begins at 0x00000000.
mem and kmem appeared
  in Version 6 AT&T UNIX.
| June 8, 1997 | NetBSD 9.4 |