All Amiga can read/write arbitrary DD and HD floppy formats, as the "controller" is actually pretty dumb, reading and writing whole tracks in magnetic flux form

All Amiga can read/write arbitrary DD and HD floppy formats, as the "controller" is actually pretty dumb, reading and writing whole tracks in magnetic flux format. The CPU (with help from Agnus's blitter in some versions of trackdisk.device) would encode/decode blocks into sectors into tracks, including MFM encoding. But the floppy drive they bundled was DD, and to get HD you needed an HD floppy drive capable of spinning at half speed. There's few models with that feature. A4000 bundled one such drive. The relevant chip (PAULA, which also was the interrupt controller and handled audio and serial port besides floppy) was sadly never upgraded throughout the history of the Amiga.