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Q72302: Specifying A20 Handlers with HIMEM.SYS /M in MS-DOS

Article: Q72302
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.x,6.0,6.2,6.21
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0, 6.2, 6.21 
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SUMMARY
=======

MS-DOS version 5.0 includes HIMEM.SYS version 2.77. MS-DOS version 6.0 includes
HIMEM.SYS version 3.07. MS-DOS versions 6.2, 6.21, and 6.22 include HIMEM.SYS
version 3.10. These versions include an A20 handler for the following computers
that can be used with the /M: or /MACHINE switch:

  CODE            Number          A20 Handler
  ----            ------          -----------
  at              1               IBM PC/AT
  ps2             2               IBM PS/2
  pt1cascade      3               Phoenix Cascade BIOS
  hpvectra        4               HP Vectra (A and A+)
  att6300plus     5               AT&T 6300 Plus
  acer1100        6               Acer 1100
  toshiba         7               Toshiba 1600 and 1200XE
  wyse            8               Wyse 12.5 MHz 286
  tulip           9               Tulip SX
  zenith          10              Zenith ZBIOS
  at1             11              IBM PC/AT
  at2             12              IBM PC/AT (alternative delay)
  css             12              CSS Labs
  at3             13              IBM PC/AT (alternative delay)
  philips         13              Philips
  fasthp          14              HP Vectra
  ibm7552         15              IBM 7552 Industrial Computer
  bullmicral      16              Bull Micral 60
  dell            17              Dell XBIOS

There are two values that are considered defaults. /M:1 is the standard default
for IBM AT-class machines, and t/M:2 is the standard default for IBM PS/2
machines. For most 100-percent-compatible machines, the /M:1, /M:11, /M:12, and
/M:13 A-20 handler switches should work. Although the other switches are
hardware specific, one may be required for proper operation on certain
machines.

NOTE: In the above list, the device driver should detect the correct handler to
use. The following computers may need the corresponding switch added to the
CONFIG.SYS file:

  System                    Switch
  ------                    ------
  Bull Micral 60            /machine:16
  COMPUADD 386 systems      /machine:1 or /machine:8
  Datamedia 386/486         /machine:2
  Hitachi HL500C            /machine:8
  Intel 301z or 302         /machine:8
  JDR 386/33                /machine:1
  Toshiba 5100              /machine:7
  UNISYS PowerPort          /machine:2

MORE INFORMATION
================

The /M switch specifies which hardware the computer is using. If the wrong
switch is used, HIMEM.SYS may not load properly or the system may hang. For more
information, query on the following words:

  HIMEM and /M

Additional query words: 6.22 5.00 5.00a 6.00 6.20

======================================================================
Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS621 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version           : MS-DOS:5.x,6.0,6.2,6.21

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