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It has been suggested that this article be merged into IMA (file format). (Discuss) Proposed since June 2011.

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The IMG file format is one of the following files:

1. A CD or DVD image file, essentially equivalent to an ISO file. On such a file, simply changing the extension from IMG to ISO can make it usable as the latter by most programs.
2. An archive format used for creating a disk image of floppy disks and HDDs. This allows for digital storage, transmission, and replication of floppy disks and HDDs. Files created using this format typically use the ".IMG" file extension. There are different, incompatible image formats which use the .IMG extension.
3. A file in the Macintosh Disk Image format used by Aladdin Systems (now Allume Systems) ShrinkWrap and Apple Disk Copy for Mac OS although they share the same file extension.
4. The IMG file format, also known as GEM IMG, is an image file format used to store bitmap digital images on Graphical Environment Manager.
5. A graphics image format used in various ways by many different graphics software packages.

IMG formats

The IMG file extension is used by files which are standardised raw dumps of a disk, and by files in various formats created by different imaging programs.

• A raw dump of the content of a disk is usually saved with the extension .IMG. This format is not compatible with the Disk Copy Fast and DiskDupe format but is supported by multiple software vendors and conventions. It contains the same data as the IMA file format. In this case the image typically 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.

• Files with the .IMG extension files are created by MS-DOS tools such as HDCopy which store the contents of a disk in a usually compressed form, different for different imaging programs: the .IMG extension is not standardised for other than raw images, and .IMG files created by different programs are not necessarily compatible. The first few bytes of the file may identify the imaging program that created it; as the file is compressed its size depends upon the contents of the image.

Support and development

The raw IMG file format is currently supported by GNU RaWrite & RaWrite2, and RawWrite for Windows. It is utilized by Qemu, VirtualBox and WinImage.

Nero Burning ROM prior to 6.0 supported reading IMG file for creating bootable CD, but since then calls them IMA.

Image files with the .IMG extension but not in raw image format are produced by several imaging programs, and are not necessarily compatible with each other, or with programs which handle raw images. There are programs which will convert between the image formats used by various programs, including raw format; one such is dsktrans from the the LibDsk suite of command-line tools for Linux, MS-DOS, and Microsoft Windows.

Programs such as ImDisk and Virtual Floppy Drive can mount a raw image of a floppy disk to emulate a floppy drive under Windows.

Accessing old floppy images in proprietary non-raw format on modern hardware can be problematical. There are some programs such as dd, a command-line program originally for Unix but ported to Microsoft Windows, which can convert images between many formats, although the syntax is rather complex. Alternatively the original program, if available, can be used either to create a physical floppy which can be used directly or re-encoded in standard raw format. Or a virtual machine can be used without the need for a physical floppy drive at all; VMware Player, for example, can mount a raw floppy image into a virtual drive A:, and the imaging program can "write" the image to the virtual floppy, thereby creating a raw image from the non-standard file. the virtual machine used must run an operating system that supports the imaging program, which may be an older Windows, Linux, MS-DOS, or any other operating system supported by the virtual hardware.

Use

IMG files are used for:

• Digital storage, transmission, and replication of floppy disks.
• Mounting virtual floppy disk volumes.

See also

• mtools

References

1. LibDsk suite of tools for accessing discs and disc image files
2. www.z80.eu: How to get the old software back to a real computer?
3. The process of converting a non-standard floppy image to raw format is a logical consequence of a virtual machine with a virtual floppy which is a raw file; "writing" an image to the "floppy" must produce a raw image. This can be confirmed by construction, using free virtualisation software such as VMWare player, the imaging software, and a virtual machine running an operating system which supports it. Simply mount an existing raw floppy image (it need not be empty), and run the imaging program with output to the virtual floppy drive; the file used in the virtual floppy will become a raw image with the same content as the proprietary one

External links

• img to iso Convert IMG disk image to ISO disk image

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