What is a Disk Image? Full Disk Imaging Explained

A disk image is an exact copy of a hard drive.  It includes all the files, the operating system, and the boot information.  Disk images can be used to recover a computer to the state it was in when the backup was made.  The primary benefit is that you don’t need to re-install the operating system or applications, thus saving time when recovering from a failed drive.

Disk image backups are often used in business environments, where downtime must be minimized in a disaster recovery scenario.

Some disk images are open file formats, such as ISO.  Other times they are proprietary formats and can only be read by the software which created them.

Disk images can be encrypted for security and compressed to save space.  They can also be created incrementally, which only backs up changes since the last backup; or differentially, which only backs up changes since the last full backup.  Since disk image backups can take up a lot of space, creating them incrementally or differentially is often preferred.

Other Uses for Disk Images

Copy & Migration

If you’ve purchased a new hard drive, you can migrate your system from the old drive without needing to re-install your software or operating system.


Virtual machines can be launched using disk images as the system drive.  The file extensions used are typically .vmdk for VMWare, .vhd for Xen and Microsoft Hyper-V, or .vdi for VirtualBox.

Because disk images used for backup and recovery are usually a different format than than those used for visualization, you must either: a.) convert the disk image to a format readable by the visualization software, or b.) use visualization software which supports the reading of the disk image file, typically with a plug-in.


Disk images can be mounted, to view the contents of the backup as if it were a drive attached to your computer.

Further Reading

Best Disk Imaging Software to Backup Your Entire Hard Drive