The Unix system call which establishes a mapping between a

range of addresses in a user process's address space and a

portion of some "memory object" (typically a file, one of the

special "devices" /dev/mem or /dev/kmem or some

memory-mapped peripheral). This allows the process to

access a file at random byte offsets without using the seek

system call or to access physical addresses or kernel's

virtual address space. It can also be used as an

alternative to writing a device driver since it is usually

simpler to code and faster to use.