Approaches for providing a guest operating system to a virtual machine. A read-only copy of one or more disk volumes, including a boot volume, is created. A copy of a master boot record (MBR) for the one or more disk volumes is also stored. The read-only copy may be, but need not be, made using a Volume Shadow Copy Service (VSS). A virtual disk, for use by the virtual machine, is created based on the read-only copy of the one or more disk volumes and the copy of the master boot record (MBR), wherein the virtual disk comprises the guest operating system used by the virtual machine. In this way, a single installed operating system may provide both the host operating system and the guest operating system.