ADF

From Classicamiga

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What is an ADF

ADF stands for Amiga Disk File.

An Amiga Disk File is a file format used by Amiga computers and emulators to store images of disks. 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.

Amiga Disk Files can actually come in a variety of different file types as shown below.

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 as only a couple of the high end Amiga models included a High Density disk drive as standard.

There are many applications available online for both the Amiga and other platforms to create and work with ADF files. And most Amiga emulators will recognise and use ADF files.

ADZ

ADZ is just a Gzipped ADF file. Apart from being compressed the files are identical and just used to save physical disk space.

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. 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, many commercial Amiga games cannot be stored in ADF files (unless modified by a cracking group), but there is an alternative called Interchangeable Preservation Format (IPF) which was specifically designed for this purpose.

The Software Preservation Society Interchangeable 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.

Many recent Amiga emulators now support the IPF file format and can load these disk images in the same way as ADFs.

DMS

DMS stands for the Disk Masher system.

It was often used on the real Amiga to create a compressed image of an Amiga disk (usually a floppy disk). The discs are read block-by-block, and their data structure maintained. In this respect the DMS file format is very similar in idea to ADF.

DMS was very popular in the Amiga Demo Scene and Game Warez Scene as a way to easily distribute Amiga disks over networks, and also to fit more than one disk onto a physical disk.

The DiskMasher format is copy protected and has problems storing some sequences of bits due to bugs in the compression algorithm, but was still widely popular on the Amiga.

For this reason many DMS compressed disk image files exist, and the most popular Amiga emulators can load DMS files in the same way as ADFs. Many Amiga Demo Scene productions and some games are often found stored as DMS files.

LHA

LHA is a freeware compression file format commonly used on the Amiga. It doesn't store disk files, but is a compression format similar to Zip or Rar. It has however been included on this page because most modern Amiga emulators can load LHA archives in the same way as they can ADFs. This is a very useful feature if you have downloaded a LHA archive containing Amiga software because you can access it in your emulator just like an ADF without first needing to find a way to extract the files.

You will most commonly encounter LHA files on Aminet

Further Information

• ADF utilities explained

References

• Wikipedia (2008) - Amiga Disk File; Wiki.
• Harrison