Tweaking the BIOS boot order under Virtual PC / Virtual Server

Tweaking the BIOS boot order under Virtual PC / Virtual Server

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Virtual PC and Virtual Server do not provide a direct user interface to allow people to change settings in the virtual machines.  The way that you change settings in the BIOS under a virtual machine is by hitting the 'DEL' key to enter the BIOS during virtual machine boot just like you would on a physical computer.

The BIOS setting information is then actually stored in the virtual machine configuration file (.VMC) under the <cmos> key.  If you are interested in changing the BIOS settings for a virtual machine in a programmatic fashion the easiest way to do this it to edit the .VMC file and replace the <cmos> key.

For an example - here is the CMOS string for a Virtual PC virtual machine with a boot order of hard disk, CD-ROM and then floppy:

<cmos type="bytes">00004050F025378002007C2F003E101000003F00000000000031004C0707070704

While this is the CMOS string for a Virtual PC virtual machine with a boot order of floppy, CD-ROM and then hard disk:

<cmos type="bytes">00004000F0203F8002001C2F00EB030600001100000000000031004C0707070703

Two things to be aware of with doing this is that the CMOS string values are only guaranteed to match when using the same revision of the same product - so you should not do this across product lines (VPC and VS) or across service pack levels (RTM and SP1) - and if you mess this information up your virtual machine may not boot :-)


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  • Oh boy, I can just see some people getting themselves in a mess with this information :)
  • Quite interesting. But makes me wonder why have such xml style file and then store "bytes" there. Couldn't you just serialize those bios options into nice human readable values :-)
  • There is really no problem doing it this way. Simply have VPC or VS generate it after you create the CMOS settings in the BIOS the regular way. Then save the different combinations off to a text file and just annotate what they were. The VPC BIOS is pretty limited. How many possible USABLE combinations can there be? Other than boot order, the only thing I've ever changed is ACPI.

  • Is there any way of doing the same thing, except instead of the boot order, changing the printer port from a regular lpt1 to an epc?
  • And I don't have any .VMC file. The only hidden file is Debian.vmsd, which is empty...

  • Just after it starts running hit Shift + ESC, it shows the post boot screen pressing Delete bring up the BIOS where changes can be made.

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