VHD (Virtual Hard Disk) is a file format which represents a virtual hard disk drive (HDD). It may contain what is found on a physical HDD, such as disk partitions and a file system, which in turn can contain files and folders. It is typically used as the hard disk of a virtual machine. The format was created by Connectix for Connectix Virtual PC product, which was later acquired by Microsoft in 2003, for what is now known as Microsoft Virtual PC. Since June 2005, Microsoft has made the VHD Image Format Specification available to third parties under the Microsoft Open Specification Promise. All virtual disk types have a minimum size of 3 MB.