1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)mem.4 8.1 (Berkeley) 06/05/93 7.\" 8.Dd 9.Dt MEM 4 vax 10.Os BSD 4 11.Sh NAME 12.Nm mem , 13.Nm kmem , 14.Nm kUmem 15.Nd memory files 16.Sh DESCRIPTION 17The special file 18.Nm /dev/mem 19is an interface to the physical memory of the computer. 20Byte offsets in this file are interpreted as physical memory addresses. 21Reading and writing this file is equivalent to reading and writing 22memory itself. 23Only offsets within the bounds of 24.Nm /dev/mem 25are allowed. 26.Pp 27Kernel virtual memory is accessed through the interface 28.Nm /dev/kmem 29in the same manner as 30.Nm /dev/mem . 31Only kernel virtual addresses that are currently mapped to memory are allowed. 32.Pp 33The file 34.Nm /dev/kUmem 35also refers to kernel virtual memory, 36but may be used to access areas mapped to 37.Tn UNIBUS 38address space 39and other 40.Tn I/O 41areas. 42It forces all accesses to use word (short integer) accesses. 43.Pp 44On the 45.Tn VAX 4611/780, 47the 48.Tn I/O 49space base address is 5020000000(16); 51on an 11/750 52the 53.Tn I/O space addresses are of the form fxxxxx(16). 54On all 55.Tn VAX Ns 'en 56the 57per-process data 58size 59for the current process 60is 61.Dv UPAGES 62long and ends at the virtual address 80000000(16). 63.Sh FILES 64.Bl -tag -width Pa -compact 65.It Pa /dev/mem 66.It Pa /dev/kmem 67.It Pa /dev/kUmem 68.El 69.Sh HISTORY 70The 71.Nm mem , 72.Nm kmem 73files appeared in 74.At v6 . 75The file 76.Nm kUmem 77appeared in 78.Bx 3.0 . 79