What is VHD?

VHD (Virtual Hard Disk) files are container formats that emulate physical hard drives for use in virtual machines. They can be fixed-size (full disk space allocated upfront), dynamically expanding (grows as data is added), or differencing (stores only changes from a parent VHD). VHD files contain complete disk structures including boot sectors, partition tables, file systems, and all data - acting exactly like physical drives to guest operating systems.

VHD is used by Hyper-V for Windows Server virtualization, VirtualBox for cross-platform VMs, legacy Virtual PC, and Azure for cloud VM storage. IT professionals use VHD for server virtualization, development environments, testing, and backups. Windows can natively mount VHD files without virtualization software. VHDX is the successor format supporting larger disks (64 TB vs 2 TB) and better resilience.

Did you know? Windows can boot directly from VHD files without virtualization!

History

Microsoft developed VHD for Virtual PC, later opening the specification and integrating it deeply into Windows and Hyper-V virtualization platforms.

Key Milestones

  • 2003: Introduced with Virtual PC 2004
  • 2006: Specification opened publicly
  • 2008: Hyper-V integration
  • 2009: Native Windows 7 mounting
  • 2012: VHDX format successor
  • Present: Still widely used format

Key Features

Core Capabilities

  • Fixed/Dynamic: Flexible allocation
  • Differencing: Parent-child chains
  • Native Mounting: Windows support
  • Bootable: Direct boot capability
  • Snapshots: Point-in-time copies
  • Cross-Platform: VirtualBox support

Common Use Cases

Virtualization

Hyper-V virtual machines

Azure VMs

Cloud virtual disks

Testing

Development environments

Backup

System image backups

Advantages

  • Native Windows support
  • Dynamic expansion saves space
  • Bootable from physical systems
  • Differencing disk chains
  • Wide software compatibility
  • Open specification
  • Easy to manage and move

Disadvantages

  • Limited to 2 TB disk size
  • Superseded by VHDX format
  • Performance overhead
  • Dynamic VHDs fragment
  • No corruption resilience
  • Older technology

Technical Information

Format Specifications

Specification Details
File Extension .vhd
MIME Type application/x-virtualbox-vhd
Max Disk Size 2 TB (2040 GB)
Types Fixed, Dynamic, Differencing
Block Size 512 bytes or 4 KB sectors
Specification Open (Microsoft published)

Common Tools

  • Virtualization: Hyper-V, VirtualBox, Virtual PC
  • Management: Disk Management (Windows), VHD Attach
  • Conversion: qemu-img, VBoxManage, StarWind V2V
  • Editing: DISM, DiskPart, 7-Zip (extract)