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The ''.img'' ] is used by files which contain raw ]s of a disk, commonly called ]s. There is no single standard for raw disk IMG files, and several different disk image formats share the same ''.img'' file extension. The actual format of the file contents will depend on the ] from which the raw disk image was created. However, the ''.img'' file format is usually associated to ] raw disk images. The ''.img'' ] is used by files which contain raw ]s of a disk, commonly called ]s. There is no single standard for raw disk IMG files, and several different disk image formats share the same ''.img'' file extension. The actual format of the file contents will depend on the ] from which the raw disk image was created. However, the ''.img'' file format is usually associated to ] raw disk images.


A similar file extension, ''.ima'', is used to refer to the same type of disk image files by some tools. A variant of the format is called called IMZ, and uses a gzipped version of a raw disk image along with the ''.imz'' file extension. Both these extensions are almost exclusively used when referring to raw disk images of floppy disks only. A similar file extension, ''.ima'', is used to refer to the same type of disk image files by some tools. A variant of the format is called IMZ, and uses a ]ped version of a raw disk image along with the ''.imz'' file extension. Both these extensions are almost exclusively used when referring to raw disk images of floppy disks only.


A typical raw floppy disk image begins with a ], where the first byte is normally hexadecimal EB (code for a 8bit short jump, offset in the 2nd byte) with third byte 90 (code for a NOP), or rarely EA (code for a 16bit jump, offset in 2nd and 3rd byte). The file size will always be a multiple of the sector size &mdash; generally 512 bytes, but other sizes such as 128 and 1024 existed. More precisely the file size corresponds to <tt><abbr title="CHS">Cylinders&times;Heads&times;(Sectors per track)</abbr></tt>, e.g., <tt>1440KB=80&times;2&times;18&times;512</tt> for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track. A typical raw floppy disk image begins with a ], where the first byte is normally hexadecimal EB (code for a 8bit short jump, offset in the 2nd byte) with third byte 90 (code for a NOP), or rarely EA (code for a 16bit jump, offset in 2nd and 3rd byte). The file size will always be a multiple of the sector size &mdash; generally 512 bytes, but other sizes such as 128 and 1024 existed. More precisely the file size corresponds to <tt><abbr title="CHS">Cylinders&times;Heads&times;(Sectors per track)</abbr></tt>, e.g., <tt>1440KB=80&times;2&times;18&times;512</tt> for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track.

Revision as of 17:14, 18 April 2013

IMG file format may refer to several different and incompatible file formats, which usually just have the use of the .img file extension in common:

This article will focus on raw disk image file formats that use the extension .img.

IMG raw disk image format

The .img file extension is used by files which contain raw dumps of a disk, commonly called disk images. There is no single standard for raw disk IMG files, and several different disk image formats share the same .img file extension. The actual format of the file contents will depend on the filesystem from which the raw disk image was created. However, the .img file format is usually associated to floppy disk raw disk images.

A similar file extension, .ima, is used to refer to the same type of disk image files by some tools. A variant of the format is called IMZ, and uses a gzipped version of a raw disk image along with the .imz file extension. Both these extensions are almost exclusively used when referring to raw disk images of floppy disks only.

A typical raw floppy disk image begins with a FAT boot sector, where the first byte is normally hexadecimal EB (code for a 8bit short jump, offset in the 2nd byte) with third byte 90 (code for a NOP), or rarely EA (code for a 16bit jump, offset in 2nd and 3rd byte). The file size will always be a multiple of the sector size — generally 512 bytes, but other sizes such as 128 and 1024 existed. More precisely the file size corresponds to Cylinders×Heads×(Sectors per track), e.g., 1440KB=80×2×18×512 for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track.

Tools

The raw IMG file format is used by several tools:

  • Tools such as RaWrite and WinImage use the IMG disk image format to read and write floppy disk images.
  • Programs such as ImDisk and Virtual Floppy Drive can mount a raw image of a floppy disk to emulate a floppy drive under Windows.
  • mtools allows manipulation of MS-DOS floppy disk images in Unix systems.
  • Nero Burning ROM supports reading IMG files for creating bootable CDs.
  • Qemu uses it as its default format for hard drive disk images.
  • Programs such as dsktrans from the LibDsk suite of command-line tools will convert between raw disk image formats, for Linux, MS-DOS, and Microsoft Windows.
  • dd can be used in Linux to create raw disk image files of disks.

References

  1. GEM Raster File Format description
  2. LibDsk suite of tools for accessing discs and disc image files
Disk image file formats
Comparison of disc image software
Optical discs
Hard disks
Floppy disks
CDDADisc Description Protocol
Convention: Any item in this table that has the form of "A+B" or "A+B+C" indicates a disk format that spans multiple files, where A contains the bulk of the data, and B and C are sidecar files.
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