Quote Originally Posted by factotum View Post
I thought it *was* a technical one, namely, that the serial chip they tried to use for the drive interface turned out not to work, so everything had to be done via the CPU? They fixed that in later revisions of the drive.
Those problems did exist, but the single biggest contributor was the IEC serial protocol. There were multiple fast-load cartridges that replaced the 1541's loaded OS (simplifying things) with a different protocol, which allowed for as much as a 5x boost in transfer speeds.