CrossDOS is a file system handler for accessing FAT formatted media on Amiga computers. It was bundled with AmigaOS 2.1 and later. Its function was to allow working with disks formatted for PCs and Atari STs (amongst others). In the 1990s it become a commonly used method of file exchange between Amiga systems and other platforms.
CrossDOS supports both double density (720 KB) and high density (1.44 MB) floppy disks on compatible disk drives. As with AmigaDOS disk handling, CrossDOS allows automatic disk-change detection for FAT formatted floppy disks. The file system can also be used with hard disks and other media for which CrossDOS provided hard disk configuration software. However, the versions of CrossDOS bundled with AmigaOS does not support long filenames, an extension to FAT that was introduced with Microsoft's Windows 95.
CrossDOS was originally developed as a stand-alone commercial product by Consultron, which was available for AmigaOS 1.2 and 1.3. In 1992 Commodore included a version of CrossDOS with AmigaOS 2.1 (and with later versions), so that users could work with PC formatted disks. In fact, the bundled version will also work with version 2.0 of AmigaOS. The bundled CrossDOS replaced an obscure tool in earlier versions of AmigaOS that could access FAT formatted disks on a secondary floppy disk drive only (this tool was not a complete file system but a user program to read files from a FAT formatted disk). Development of CrossDOS continued after being bundled with the OS. CrossDOS 7 was the last version released which includes support for long filenames amongst other features not available in the bundled version.