It wasn't really the hardware's fault though. It was crippled by Commodore's marketing department wanting to maintain compatibility with the VIC-20's 1540 FDD, which meant that the bit banging method used to work around a bug in the VIA chip had to be used. Then to add insult to injury, because of how the VIC-II and 6510 need to share the bus, it ended up running even slower than the VIC-20.