page_title: Floppy disk variants
section_title: Commodore Amiga
hierarchical_section_title: Floppy disk variants / Custom formatting types on 3½-inch and 5¼-inch media / Commodore Amiga
caption_attribution_description: Amiga Custom Chip Paula 8364 (im Amiga 1200)
context_page_description: The floppy disk is a data storage and transfer medium that was ubiquitous from the mid-1970s well into the 2000s. Besides the 3½-inch and 5¼-inch formats used in IBM PC compatible systems, or the 8-inch format that preceded them, many proprietary floppy disk formats were developed, either using a different disk design or special layout and encoding methods for the data held on the disk.
context_section_description: The Commodore Amiga computers use an 880 KB format (11×512-byte sectors per track, times 80 tracks, times two sides) on a 3½-inch floppy. Because the entire track is written at once, intersector gaps can be eliminated, saving space.  The Amiga floppy controller is basic but much more flexible than the one on the PC: it is free of arbitrary format restrictions, encoding such as MFM and GCR can be done in software, and developers were able to create their own proprietary disk formats. Because of this, foreign formats such as the IBM PC-compatible can be handled with ease (by use of CrossDOS, which was included with later versions of AmigaOS). With the correct filesystem driver, an Amiga can theoretically read any arbitrary format on the 3½-inch floppy, including those recorded at a slightly different rotation rate. On the PC, however, there is no way to read an Amiga disk without special hardware, such as a CatWeasel, and a second floppy drive.
  Commodore never upgraded the Amiga chip set to support high-density floppies, but sold a custom drive (made by Chinon) that spins at half speed (150 RPM) when a high-density floppy was inserted, enabling the existing floppy controller to be used. This drive was built into the Amiga 3000, although the later Amiga 1200 was only fitted with the standard DD drive. The Amiga HD disks can handle 1760 KB, but using special software programs they can hold even more data.  A company named Kolff Computer Supplies also made an external HD floppy drive (KCS Dual HD Drive) available which can handle HD format diskettes on all Amiga computer systems.
  Because of storage reasons, the use of emulators and preserving data, many disks were packed into disk images. Currently popular formats are .ADF (Amiga Disk File), .DMS (DiskMasher) and .IPF (Interchangeable Preservation Format) files. The DiskMasher format is copy-protected and has problems storing particular sequences of bits due to bugs in the compression algorithm, but was widely used in the pirate and demo scenes. ADF has been around for almost as long as the Amiga itself though it was not initially called by that name. Only with the advent of the internet and Amiga emulators has it become a popular way of distributing disk images. The proprietary IPF files were created to allow preservation of commercial games which have copy protection, which is something that ADF and DMS cannot do.
  The Amiga is also notorious for the clicking sound made by the floppy drive mechanism if no disk is inserted. The purpose is to detect disk changes, and various utilities such as Noclick exist that can disable the clicking noise to the relief of many Amiga users.
caption: The pictured chip, codenamed Paula, controls floppy access on all revisions of the Commodore Amiga as one of its many functions
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