BSD 2.11 - man page for mem (bsd section 4)

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MEM(4)											   MEM(4)

       mem, kmem - main memory

       major device number(s):
	    raw: 1
       minor device encoding:
	    mem: 0;  kmem: 1;  null: 2

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

       On PDP-11s, the I/O page begins at location 0160000 of kmem and the per-process data  seg-
       ment for the current process begins at 0140000 and is USIZE clicks (64 bytes each) long.

       /dev/MAKEDEV	   script to create special files
       /dev/MAKEDEV.local  script to localize special files

       On PDP-11's, specifying an odd kernel or user address, or an odd transfer count is [gener-
       ally] slower than using all even parameters.

       On machines with ENABLE/34(tm) memory mapping boards the I/O page  can  be  accessed  only
       through kmem.

3rd Berkeley Distribution		 January 28, 1988				   MEM(4)
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