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At a hardware level, the DivIDE provides a 16 bit [[:wikipedia:Parallel_ATA|parallel ATA]] interface. Higher level capabilities (such as access to PC filesystems and loading emulator files) are handled in firmware written to the onboard Flash ROM - the DivIDE provides hooks into various points in the Spectrum ROM, such as the tape load/save routines, meaning that disk access can be closely integrated into Spectrum BASIC. There are a variety of firmware images available, offering different features:
http://esxdos.org/ ESXDOS], by Phoenix, is an operating system providing read/write access to FAT16 and FAT32 filesystems, and the ability to load emulator snapshot / tape files, via extended BASIC syntax and a menu-driven file launcher. It also emulates the TR-DOS disk system (used by the majority of Russian software).
* FATware, by Baze, works with FAT16-formatted disks and provides a friendly menu-driven interface for launching emulator snapshot and tape files, including support for long filenames. However, disk access is read-only, and there's no provision for accessing the filesystem directly from user code.
* [https://www.worldofspectrum.org/residos/ ResiDOS], by Garry Lancaster, runs on the DivIDE Plus and extends BASIC with commands for disk access, along with various additional tools and packages including a task manager, simple windowing facilities and emulators for the ZX80 and ZX81. It primarily works with [[IDEDOS]] filesystems, but FAT support is available in an add-on package.