sector size. For floppy disks and hard drives this size is typically 512 bytes (but other sizes such as 128 and 1024 exist). More precisely, the file size of a raw disk image of a magnetic disk corresponds to: Cylinders × Heads × (Sectors per track) × (Sector size) E.g. for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track: 80 × 2 × 18 × 512 = 1,474,560 bytes or 1440 KB For optical discs such as CDs and DVDs, the raw sector size is usually 2,352, making the size of a raw disc image a multiple of this value. Comparison to ISO images ISO images are another type of optical disc image files, which commonly use the .iso file extension, but sometimes use the .img file extension as well. They are similar to the raw optical disc images, but contain only one track with computer data obtained from an optical disc. They cannot contain multiple tracks, nor audio or video tracks. They also do not contain the control headers and error correction fields of CD-ROM or DVD sectors that raw disc images usually store. Their internal format follows the structure of an optical disc file system, commonly ISO 9660 (for CDs) or UDF (for DVDs). The CUE/BIN and CCD/IMG formats, which usually contain raw disc images, can also store ISO images instead. IMG as an image file format .img is also a planar bitmap graphics file using simple run-length encoding, originating with Digital Research's GEM. It was commonly used on the Atari ST line of home computers, but also with some GEM-based PC software such as Corel Ventura or Timeworks Publisher. Other disk image files In addition, .img is an Apple Disk Image used by the Mac OS X or macOS operating system. Garmin .img is a hard-disk image file format which contains a header and many subfiles and used to store the maps for its GPS units. Tools The raw IMG file format is used by several tools: RaWrite and WinImage use the IMG disk image format to read and write floppy disk images. ImDisk and Virtual Floppy Drive can mount a raw image of a floppy disk to emulate a floppy drive under Microsoft Windows. Nero Burning ROM supports reading IMG files for creating bootable CDs. mtools allows manipulation of MS-DOS floppy disk images in Unix systems. Programs such as dsktrans from the