Patent ID: 6968350

Claim:
A method for performing a write operation to a virtual hard drive of an emulated computer system, comprising the steps of: establishing in a hard drive of a host computer system a plurality of files comprising the virtual hard drive of the emulated computer system, the plurality of files including a file associated with a parent drive and a file associated with a differencing drive, the parent drive appearing to the emulated computer system to be a physical hard drive of the emulated computer system; and the differencing drive comprising a bit map that identifies blocks of the virtual hard drive that are present in the differencing drive; performing a write operation in the emulated computer system to the virtual hard drive of the emulated computer system; and recording a result of the write operation in the differencing drive of the virtual hard drive such that write operations performed to the virtual hard drive of the host computer system are performed in the differencing drive rather than in the parent drive.