1MEM(4)                     Kernel Interfaces Manual                     MEM(4)
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NAME

6       mem, kmem - main memory
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SYNOPSIS

9       major device number(s):
10            raw: 1
11       minor device encoding:
12            mem: 0;  kmem: 1;  null: 2
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DESCRIPTION

15       Mem  is  a special file that is an image of the main memory of the com‐
16       puter.  It may be used, for example, to examine (and even to patch) the
17       system.
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19       Byte  addresses  in  mem  are interpreted as physical memory addresses.
20       References to non-existent locations cause errors to be returned.
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22       The file kmem is the same as mem  except  that  kernel  virtual  memory
23       rather than physical memory is accessed.  Only kernel virtual addresses
24       that are mapped to memory are allowed.  Examining and  patching  device
25       registers  is  likely  to  lead to unexpected results when read-only or
26       write-only bits are present.
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28       On PDP-11s, the I/O page begins at location 0160000  of  kmem  and  the
29       per-process  data segment for the current process begins at 0140000 and
30       is USIZE clicks (64 bytes each) long.
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FILES

33       /dev/mem
34       /dev/kmem
35       /dev/MAKEDEV        script to create special files
36       /dev/MAKEDEV.local  script to localize special files
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BUGS

39       On PDP-11's, specifying an odd kernel or user address, or an odd trans‐
40       fer count is [generally] slower than using all even parameters.
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42       On  machines  with ENABLE/34(tm) memory mapping boards the I/O page can
43       be accessed only through kmem.
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473rd Berkeley Distribution      January 28, 1988                         MEM(4)