Disk images, in computing, are computer files containing the contents and structure of a disk volume or an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc or USB flash drive. A disk image is usually made by creating a sector-by-sector copy of the source medium, thereby perfectly replicating the structure and contents of a storage device independent of the file system. Depending on the disk image format, a disk image may span one or more computer files.