[Two9A]

It's worse than that even: there are delays after every _bit_ transferred, due to various design decisions that were made along the way, which is why the C64's disk drive is slower than the previous computer (the VIC-20), which is slower than the one before that (the PET).

I wrote about the decisions and the resulting delays for one of those 100-post Threadapalooza projects in 2024, compiled here for easier reading: https://imrannazar.com/articles/commodore-1541

[krige]

> A minor rework of the board at the board manufacturers (to accommodate a screw hole, I believe) accidentally discarded the high-speed wire.

oh my

[rasz]

Not buying that, C64 had like 5-10 pcb revisions so spinning another one wouldnt be extraordinary, and in the mean time they could put bodges on old stock pcbs or you know, supply USERPORT cable as thats where 6526 is wired to. Original Kernal has no traces commodore ever tried to use hardware shift register, they simply left VIC20 bodge and didnt even try accommodating fixed 6526.

[krige]

Memory a bit foggy on that but weren't c64 mainboard revisions almost exclusively to make them cheaper, not better?

[rasz]

Successive revisions fixed hardware bugs and added functionality like 8-pin video port in place of 5-pin one.