Virtual PC has 2 ways of implementing rollback. The first way is through a type of virtual hard drive called a Differencing disk. A Differencing disk stores only the changes made against an existing hard drive image. The virtual machine sees a Differencing disk as a normal hard drive.
The second way is through Undo disks. When you enable Undo disks in the virtual machine settings in Virtual PC, it stores all changes made while a virtual machine is running to a separate file. When you shut down or suspend a virtual machine, you can choose to write the changes to the actual hard drive image, discard the changes, or temporarily keep the changes without writing them to the hard drive. If a virtual machine has multiple hard drives, the chosen action applies to all the hard drives.
Last edited: May 28, 2006
