Disk image

A disk image is a single computer file containing the complete contents of a device that contains data, such as a hard drive, tape drives, floppy disk, CD, DVD, BD, and key drive. 
A disk image file (or simply a disk image) is an exact binary copy of an entire disk or drive. Disk image files contain all the data stored on the source drive including not only its files and folders but also its boot sectors, file allocation tables, volume attributes and any other system-specific data. A disk image is not a collection of files or folders but is an exact duplicate of the raw data of the original disk, sector by sector.