IMG (file Format) - IMG Formats

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.