Amiga Disk File
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Amiga Disk File aka ADF is a file format used by Amiga computers and emulators to store images of disks. It has been around almost as long as the Amiga itself, although it was not initially called by any particular name. Before it was known as ADF, it was used in commercial game production, backup and disk virtualization. Technically speaking, ADF is not really a file format but actually a track-by-track dump of the disk data as read by the Amiga operating system, and so the "format" is really fixed-width AmigaDOS data tracks appended one after another and held in a file.
Most ADF files are images of the Amiga-formatted tracks held on cylinder 0 to 79 of a standard 3.5" Double Density floppy disk, also called an 880KB disk in Amiga terms. The size of an ADF will vary depending on how many tracks have been imaged, but in practice it is unusual to find ADF files that are not 901120 bytes in size.
Most Amiga programs were distributed on Double Density floppy disks. There are also 3.5" High density floppy disks which hold up to 1.76 MB of data but these are uncommon. The Amiga also had 5.25" Single Density disks. The WinUAE Amiga emulator supports all 3 disc formats but 3.5" DD is the most common.
There is also an ADF file format called ADZ which is a Gzip compressed ADF file.
The ADF file format can only store disks that have legal AmigaDOS format tracks. The Amiga's Floppy Disk Controller was very basic, but also very flexible. Disk handling is not completely locked down like the one in a modern PC, and so most of the work to read and write disks is done by the operating system itself. However, because programmers did not have to use the operating system routines, it was quite normal for games developers to create their own disk formats and also apply many different sorts of copy protection. As it was, most full-price commercial Amiga games had some form of custom disk format and/or copy protection on them. For this reason, most commercial Amiga games cannot be stored in ADF files, but there is an alternative called IPF (Interchangeable Preservation Format) which was specifically designed for this purpose.
There is a program called ADF Opus which is a Windows-based program which allows people to create their own ADF files. This program supports creating Double Density ( 880 KB ADF files. This is the most common) & High Density (1.76 MB ADF files). ADF Opus also allows people to convert ADF files into ADZ files.
