The Commodore 1541 floppy disk drive was notoriously slow, primarily due to the slow serial interface connecting the external drive to the C64. 1541 zip performed a "fast copy" by downloading new 6502 firmware into the disk drive with matching 6502 assembly language software that ran on the C64. 1541 zip wasn't the first program to do this, but it was one of the first, and I am pretty proud of it. It was very tricky to figure out how to re-program the 1541 - I had very sparse documentation. And I had no tools (like an oscilloscope) to monitor the serial lines to aid in debugging. As well as using a faster transmission protocol that I designed, I also timed the rotation of the drive so I could read and send more than one sector per rotation.
I have a rejection letter from Ahoy! (it seems to have been sent late, as I think I wrote this program earlier). I recall it was also rejected by "the Transactor" - a more technical C64 publication. I ran into the Jim Butterflied - former editor of Transactor - a few years later at an Amiga conference, and asked him why they rejected it. He said that my article that explained how it worked was too short.
