Microsoft KB Archive/72302

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

Article ID: 72302

Article Last Modified on 11/26/2003

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APPLIES TO


 * Microsoft MS-DOS 5.0 Standard Edition
 * Microsoft MS-DOS 5.0a
 * Microsoft MS-DOS 6.0 Standard Edition
 * Microsoft MS-DOS 6.2 Standard Edition
 * Microsoft MS-DOS 6.21 Standard Edition

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This article was previously published under Q72302



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: KB72302

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