DAT cassettes aren't interchangeable with audio cassettes. DAT tape shells are smaller, and the helical (not linear) recording was digital. The cassettes were drawn into the deck, horizontally, on a tray.
DAT never had much impact in the consumer market, but was "the standard" for small recording medium in the pro audio world, the way BetaCam SP was in the video world.
I still have an awesome Tascam deck in my rack that I used when I needed to make live, longer-than-74-minute recordings than my Tascam CD Recorder could make, or when a voiceover actor was in the soundbooth...as it allowed me to place "markers" along the recording to mark good/bad takes.
