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.