Disk and VM image file formats

A disk image is a whole disc or hard disk stored as one file, sector by sector, with its partitions and file systems inside. Optical disc images are burned or mounted. Virtual disk images act as the hard disk of a virtual machine, and many of them only store the parts of the disk that have been written.

Formats

.DMG

Apple disk image

The Mac’s disk image: compressed runs of sectors and a koly trailer.

.IMG

Raw disk image

A disk or memory card copied byte for byte, with no header.

.ISO

ISO 9660 disc image

A CD, DVD or Blu-ray copied sector by sector into one file.

.QCOW2

QEMU copy-on-write disk image

QEMU’s growable virtual disk with snapshots and backing files.

.VDI

VirtualBox Disk Image

VirtualBox’s virtual disk: a header, a block map and the written blocks.

.VHD

Virtual Hard Disk

Microsoft’s virtual machine disk: raw or dynamic data with a 512-byte footer.

.VHDX

Hyper-V virtual hard disk

VHD’s successor: up to 64 TB, with a log that survives power failures.

.VMDK

VMware Virtual Machine Disk

VMware’s virtual disk: a text descriptor and flat or sparse extents.