Although the PET is most likely the more well-known of Commodore’s early computer systems ... adding a floppy drive like the ubiquitous 1541 with its IEC bus interface was not a first-party ...

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.