

Likewise, when restoring data from a clone of a hard drive you will boot from the cloning software CD. This is necessary because the cloning software cannot copy operating system files on the hard drive while they are in use, and because you want the hard drive's contents completely "at rest" when you take a snapshot of it. You reboot your computer from the cloning software CD (or other external media). Hard disk cloning software (disk imaging software) includes its own minimal operating system. If something goes wrong with your hard drive, a clone copy (disk image) can restore its exact contents at a certain point in time to the same or another hard drive. This is one good reason to make your own backup image copy every now and then. But at least you have a working system that's not fouled up with malware or registry errors. Of course, all your personal settings user-installed software and personal data files are not restored.

Restoring the contents of the rescue disk returns the hard drive to its factory-new state.

The "rescue disk" that comes with some computers is a clone of the computer's hard drive as it was at the time it was shipped by the manufacturer. Wherever the disk image is stored, having access to the whole disk image or just individual files in it is an excellent safety net against hard drive crashes. It can be stored on a network drive, a web server, or in cloud storage. A disk image can be stored on a hard drive, or offline media such as DVDs. Think of it as a snapshot of your hard drive. A hard drive clone or image is often stored as a single, huge file called a "disk image" file.
