The Commodore 64 was the worlds most popular home computer, there were millions sold, have you tried googling for it? - there's plenty of information out there!.
I've no idea what the 'fastdisk' you refer to is, but the standard 64 floppy drive is so slow it's unbelieveable! - the Sinclair Spectrum cassette interace is considerably faster :lol:
The reason comes from the VIC20 (the 64's predecessor), the story goes that they spent so much money developing the VIC20 that the interface where the floppy plugs in (some weird serial interface), was just thrown together at the last minute, with no money left to do it properly.
As the 64 used the same disk drive (1541 if I recall correctly?), it was given the same crappy interface.
I had a PLUS 4 (and still have, somewhere?), these could use the 1541 drive (and were just as slow), but they had their own faster drive, which was many times faster than the 1542 and used a different parallel interface (but still pitifully slow compared to modern floppies).