Disk cloning

Disk cloning is the process of copying the contents of one computer hard disk to another disk or to an "image" file. This may be done straight from one disk to another, but more often, the contents of the first disk are written to an image file as an intermediate step, then the second disk is loaded with the contents of the image. Typically, this is done for archiving purposes, to restore lost or damaged data, or to move wanted data into a new disk, though other reasons also exist.

Unlike standard copying functions, disk cloning involves copying hidden and in-use files, and thus presents special challenges, as those types of files are typically not available for copying. Additional complications arise when the process is used for networked computers, as the network must be able to distinguish between different computers. Post-cloning operations may be necessary to address these and other issues.

There are a number of notable uses for disk cloning software. These include:

This article is specific to disk cloning on the x86 and PowerPC platform; specific details may not apply to other platforms.

To provision the hard disk of a computer without using disk cloning software, the following steps are generally required for each computer:

With disk cloning, this is simplified to:

This can be referred to simply as a recovery disc.

Before Windows 95, some computer manufacturers used hardware disk copying machines to copy software. This had the disadvantages of copying not just the used data on the disk, but also unused sectors, as the hardware used was not aware of the structures on the disks. A larger hard disk could not be copied to a smaller one, and copying a smaller one to a larger left the remaining space on the new disk unused. The two disks required identical geometries.

Other manufacturers and companies partitioned and formatted disks manually, then used file copy utilities or archiving utilities, such as tar or zip to copy files. It is not sufficient simply to copy all files from one disk to another, because there are special boot files or boot tracks which must be specifically placed for an operating system to run, so additional manual steps were required.

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