IMG (file format)

An IMG file, a.k.a. raw disk image, contains a complete and uncompressed disk image of a storage device's data content. The image includes the value of each memory location of the storage device, ordered sequentially such that the data can be written to a similar device to completely overwrite its content. The layout of data in a raw image depends on the file system of the target storage device (for example FAT). For example, an optical disc (i.e. CD or DVD) raw image contains the tracks of audio or video. In the case of a CD-ROM or DVD, an image usually includes not only the data of each sector, but the control headers and error correction fields for each sector as well. Since raw image files hold no additional data ("metadata") beyond the storage content, determining the structure of an existing image can be difficult. Either a user remembers what a file contains via their memory or records metadata in the file name or via some other mechanism. In some cases, a tool can detect aspects of an image file's content. For example, a typical floppy disk raw image begins with a FAT boot sector, which can be used to identify the file system. A raw optical disc image is usually accompanied by a separate file which describes the layout of the image data, including information such as track limits which are not in the raw image.