Amiga Disk File

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.

ADF

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 880 KB 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 (80 cylinders x 2 heads x 11 sectors x 512 bytes/sector).

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" double density discs. The WinUAE Amiga emulator supports all 3 disc formats but 3.5" DD is the most common.

ADF files can be downloaded and copied to Amiga disks with the EasyADF application and various applications freely available on the internet.

There is a program called [http://adfopus.sourceforge.net/ ADF Opus] which is a MS-Windows-based program which allows people to create their own ADF files. This program supports creating Double Density (880 KB ADF files, the most common) and High Density (1.76 MB) ADF files. ADF Opus also allows people to convert ADF files into ADZ files.

There is also a GNU GPL command line program called [http://lclevy.free.fr/adflib/unadf.html unADF] that allows you to extract files from a .ADF archive.

ADZ

ADZ files is an ADF file format which is just Gzip compressed.

IPF

The ADF file format can only store disks that have legal AmigaDOS format tracks. The Amiga's floppy disk controller was very basic but transparent, and for that reason very flexible allowing disks of other and custom formats to be read and written as well. Disk handling is not 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 [cite web|title=Software Preservation Society - Glossary|url=http://www.softpres.org/glossary:fdc 070820 softpres.org] . 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 [cite web|title=Software Preservation Society - Glossary|url=http://www.softpres.org/glossary:custom_disk_format 070820 softpres.org] and also apply many different sorts of copy protection [cite web|title=Software Preservation Society - Glossary|url=http://www.softpres.org/glossary:copy_protection 070820 softpres.org] . 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 [http://www.softpres.org/ Interchangeable Preservation Format] (IPF) which was specifically designed for this purpose.

The Software Preservation Society Interchangable Preservation Format (.IPF) is an undocumented IFF file format which can only be read (not written) via a proprietary closed source .dll or other library file. Creation of IPF files is entirely restricted to the SPS themselves, using their own private disk analysis software.

References

* [http://www.amigau.com/aig/adfaq.html Amiga History Guide, The .ADF (Amiga Disk File) format FAQ]
* The Amiga Guru Book, Chapter 15, Ralph Babel, 1993
* Rom Kernel Reference Manual : Hardware, pages 235-244, Addison Wesley
* Rom Kernel Reference Manual : Libraries and Devices, Appendix C, Addison Wesley
* La Bible de l'Amiga, Dittrich/Gelfand/Schemmel, Data Becker, 1988.

See also

* Floppy disk