Once upon a time, you might have developed for the Commodore 64 using the very machine itself. You’d use the chunky old keyboard, a tape drive, or the 1541 disk drive if you wanted to work faster.

IC and an EPROM featuring the new code to support the proprietary Commodore IEC bus protocol, which was mostly pilfered byte-for-byte from a C64 kernal ROM. With some creative breadboarding in ...