+.TH MEM 4
+.SH NAME
+mem, kmem \- main memory
+.SH DESCRIPTION
+.I 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.
+.PP
+Byte addresses in
+.I mem
+are interpreted as physical memory addresses.
+References to non-existent locations cause errors to be returned.
+.PP
+Examining and patching device registers is likely
+to lead to unexpected results when read-only or write-only
+bits are present.
+.PP
+The file
+.I kmem
+is the same as
+.I mem
+except that kernel virtual memory
+rather than physical memory is accessed.
+.PP
+On PDP11's, the I/O page
+begins at location 0160000 of
+.I kmem
+and per-process data for the current process
+begins at 0140000.
+On VAX11's the I/O space begins at physical address 20000000(16)
+and per-process data for the current process is at virtual 80020000(16).
+.SH FILES
+/dev/mem,
+/dev/kmem
+.SH BUGS
+On PDP11's and VAX11's, memory files are accessed one byte
+at a time, an inapproriate method for some
+device registers.