XenServer hangs on Himem.sys when booting DOS

XenServer hangs on Himem.sys when booting DOS

I am testing out XenServer for server virtualization, and Acronis for physical-to-virtual conversions. When booting on the Acronis restore CD, the vm displays:

cirrus-compatible VGA is detected
Processor 1: Xen(R) Virtual CPU
XS Virtual IDE Controller  Hard Drive (16384MB)
Unknown device
Unknown device
XS Virtual ATAPI-4  CD-Rom/DVD-Rom

Boot device: CD-Rom – success.
Starting Caldera DR-DOS…
HIMEM.SYS: Cannot control address line A20.

Caldera DR-DOS 7.03
Copyright (c) 1976, 1998 Caldera, Inc. All rights reserved.

It then hangs with the processor consuming 100% of the resources. I notice the same behavior when booting from a DOS 6.22 disk with Himem.sys loading, even if I specify /a20control:off.  I found an article from Microsoft that describes the problem. Submitted it to Acronis to get a fix. They wrote back “We have confirmed this behavior with the Xen Virtualization platform with the DR process. Right now it has been logged as a defect in our bugtracker. Right now I do not have an ETA on this being resolved.”

 The “Unable to control A20 Line” error message

There are two workarounds for this problem:

Add the /M:x switch to the HIMEM.SYS line in the CONFIG.SYS file, where x is number from the valid range of 1-14 and 16, and then restart your computer. For example: DEVICE=C:\DOS\HIMEM.SYS /M:1

Upgrade your computer’s BIOS or contact your computer vendor for help with the modification of your CMOS settings. You may need to disable a FastGate (or similar) option.

The A20 line is the start of the first 64K of extended memory, known as the high memory area (HMA). The HIMEM.SYS device driver must control the A20 line to manage extended memory. The HIMEM.SYS driver reports the error if it incorrectly identifies the extended memory handling mechanism of the computer or if the handling method of the computer’s BIOS is unknown.

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