NAME

mem, kmem, vmem − main memory

DESCRIPTION

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. 

Examining and patching device registers is likely to lead to unexpected results when read-only or write-only bits are present. 

The file kmem is the same as mem except that kernel virtual memory rather than physical memory is accessed. 

The file vmem is the same as mem except that video memory, which holds the bitmap image of the screen, is accessed. 

On the IS68K the LSI-11 Bus I/O page begins at location 0x3FE000 of kmem and per-process data for the current process begins at 0x3FD00. 

The mmap(2) system call may be applied to the mem file to obtain direct access to physical memory or device registers. 

FILES

/dev/mem
/dev/kmem
/dev/vmem

BUGS

Memory files are accessed one byte at a time, an inappropriate method for some device registers. 

4th Berkeley Distribution  —  1 August 1985