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

# NAME

`mem`, `kmem`, `kUmem` —
memory files

# DESCRIPTION

The special 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. Only offsets within the bounds of `/dev/mem` are allowed.

Kernel virtual memory is accessed through the interface `/dev/kmem` in the same manner as `/dev/mem`. Only kernel virtual addresses that are currently mapped to memory are allowed.

The file `/dev/kUmem` also refers to kernel virtual memory, but may be used to access areas mapped to UNIBUS address space and other I/O areas. It forces all accesses to use word (short integer) accesses.

On the VAX-11/780, the I/O space base address is 20000000(16); on an 11/750 the I/O space addresses are of the form fxxxxx(16). On all VAX'en the per-process data size for the current process is `UPAGES` long and ends at the virtual address 80000000(16).

# FILES

/dev/mem
/dev/kmem
/dev/kUmem

# HISTORY

The `mem`, `kmem` files appeared in Version 6 AT&T UNIX. The file `kUmem` appeared in 3.0BSD.

June 5, 1993 | NetBSD 10.1