FOSDEM 2025 – Raiders of the lost hard drive

In 1984 Commodore introduced the C900, a budget Unix workstation with an obscure Zilog Z8000 processor. Unfortunately, when hey bought the Amiga, the Commodore 900 project was canceled and today only a few dozen prototypes exist.

A few years ago I happened to get one of these prototypes. Without a working power supply, monitor, keyboard and with the hard drive giving a mysterious 0xFF error, I was left puzzling on how to make the machine run.

This talk documents my successful effort to bring the machine back to life. It is a continent-spanning tale of digital archaeology, which included, among others, disassembling the Z8000 BIOS, reverse-engineering the keyboard interface and figuring out the hard disk low level format. After I figured out how to make the machine run, I have helped two other Commodore 900 owners with the same problems to make their machines fully working.