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@(#)mem.4 6.2 (Berkeley) 05/16/86

C 4 mem, kmem - main memory .lg Mem is a special file that is an image of the main memory of the computer. It may be used, for example, to examine (and even to patch) the system.

Byte addresses in mem are interpreted as physical memory addresses. References to non-existent locations cause errors to be returned.

The file kmem is the same as mem except that kernel virtual memory rather than physical memory is accessed. Only kernel virtual addresses that are mapped to memory are allowed. The file 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. Examining and patching device registers is likely to lead to unexpected results when read-only or write-only bits are present.

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

/dev/mem

/dev/kmem

/dev/kUmem