MEM(4) | Device Drivers Manual (hp300) | MEM(4)

# NAME

`mem`, `kmem` — main memory

# DESCRIPTION

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.

# HP300

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`.

# FILES

/dev/mem
/dev/kmem

# HISTORY

The files `mem` and `kmem` appeared in Version 6 AT&T UNIX.

June 5, 1993 | NetBSD 11.0