HIMEM.SYS Err Msg: ERROR: Can't Enable A20

Last reviewed: November 23, 1994
Article ID: Q89699

The information in this article applies to:

Microsoft Windows operating system versions 3.0, 3.0a, 3.1, 3.11

SYMPTOMS

You may see one of the following error messages when youstart your system:

   ERROR: Can't enable A20!

   -or-

   WARNING: The A20 Line Was Already Enabled.

CAUSE

These error messages indicate that HIMEM.SYS is unable to control the A20 gate and affect the extended-memory handling system in your computer.

The following can cause these errors to occur:

You are loading another memory manager or device driver before loading HIMEM.SYS, and it is not allowing HIMEM.SYS access to the A20. Try making a bootable system floppy, and in the CONFIG.SYS file make sure that HIMEM.SYS is the first device loaded.
HIMEM.SYS has incorrectly identified the extended-memory handling mechanism on your computer. Try specifying an alternate A20 handler by using the /M: command line parameter from a bootable system floppy.
Windows 3.0 HIMEM.SYS Version 2.60 ----------------------------------
Refer to the README.TXT file that is located in your Windows directory.
Windows 3.0 with MS-DOS 5.0 HIMEM.SYS Version 2.77 --------------------------------------------------
Refer to the README.TXT file that is located in your DOS directory and to page 610-613 of the "Microsoft MS-DOS User's Guide and Reference" for version 5.0.
Windows 3.1 HIMEM.SYS Version 3.07 ----------------------------------
Refer to pages 543-547 of the "Microsoft Windows User's Guide."
MS-DOS 6.0 and 6.2 Systems --------------------------
Refer to pages 217-220 of the Microsoft MS-DOS User's Guide for version 6.0 and 6.2.
The machine's BIOS uses an extended-memory handling method that is unknown to HIMEM.SYS.
- If the BIOS is shadowing ROM, then contact your hardware vendor
```
     and see if this option can be disabled to allow HIMEM.SYS to load.
```
- If the BIOS is doing any special handling of the A20, then
```
     contact your hardware vendor and see if this option can be disabled
     to allow HIMEM.SYS to load.
```
- In some cases, a BIOS upgrade from the manufacturer may solve the
```
     problem.
```

KBCategory: kbother kberrmsg
KBSubcategory: win30 win31
Additional reference words: err msg winboot 3.10 3.00a 6.00 6.20 3.00 3.11
himemver extended memory

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Last reviewed: November 23, 1994
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