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Using an "undo" disk on Virtual PC 2007, when the VPC is shut down, the program will ask, "Do you want to merge the change into the main virtual hard drive, or discard the change, or to save the change into a separate file".

But on Windows 7's Virtual PC, I tried using the same images as above, from the website

but this time, when I shut down the virtual PC, there was no question asked. The undo file (.vud) keeps on growing each time I boot up and shut down, and the original .vhd remains intact. Is there something that can be done to merge, or discard those changes? The .vud file is now about 1.2GB large.

Update: seems like no one knows an answer yet?

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up vote 5 down vote accepted

There is a separate option to do this in the VM's settings. See here for details:

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i think the setting is already with "undo" disk, coz otherwise there won't be .vud file and its size changing as I use the virtual machine. – 太極者無極而生 Nov 4 '09 at 18:21
Expanded to link which talks about the move from a shutdown option to a separate (settings based) merge option. – Richard Nov 5 '09 at 8:33
ok, that's true... go to "Settings" and then "Undo Disk" and you will see the option to delete it. – 太極者無極而生 Nov 14 '09 at 3:05

Here is some info from the VPC help file on Win 7:

If the virtual machine is running or hibernated, shut it down. For instructions, see Shut down a virtual machine manually.

Open the Virtual Machines folder.

Right-click the name of the virtual machine, and then click Settings.

In the left pane of Windows Virtual PC Settings, click Undo Disks.

In the right pane, click either Apply changes or Discard changes, and then click OK.

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