A VHD (Virtual Hard Disk) file is a disk image format that represents a virtual hard drive. It essentially acts as a container for all the data that would reside on a physical hard drive, including files, folders, operating systems, and applications. VHD files are commonly used in virtualization environments, allowing users to run multiple operating systems on a single physical machine. They enable the creation of virtual machines (VMs) that can be easily deployed, backed up, and restored. The VHD format is supported by various virtualization platforms, including Microsoft Hyper-V, VirtualBox, and VMware. VHDs can be mounted as drives on a host operating system, allowing users to access and modify the files within the virtual disk. They are also used for software testing, disaster recovery, and creating portable application environments. The format supports both fixed-size and dynamically expanding virtual disks, offering flexibility in storage allocation. VHDX is a newer version of the VHD format that supports larger virtual disk sizes and improved data protection features.