Commodore 900 / C900 / Z-8000 [Prototype]

Found after decades in March 2026 in an unstable attic in a house at risk of collapsing, this is the true “untested attic find”.

Also known as the “Z-Machine” for its processor, the Commodore 900 never left the prototype state. Most sources talk about only 50 units built. Classified as a mainframe computer, the 900 runs a version of UNIX called “Coherent” in order to give it its multi-tasking and multi-user capabilities.
The Commodore 900 (also called the Z-8000 on early design materials) came in two variants: Model 1 [the server], and Model 2 [the workstation].
The workstation offers the high-res video capabilities the server lacks, which in turn has more I/O ports. Apart from the sandwich video board both machines are identical.

This model is the server version with the low-res video board and the two extra serial ports.

Currently the machine is undergoing full testing and restoration.

• CPU: Zilog Z-8001, 16 Bit
• Clock Speed: 10MHz
• Operating System; Coherent
• RAM: 512kB [expandable up to 2MB]
• ROM: 32kB
• Text mode: 80×25 monochrome
• Sound: Beeper/Speaker
• HDD: Seagate ST-225 20MB [via separate controller board]
• FDD: 1,2 MB 5,25″ Matsushita JA-560-012 [directly connected to the main board]
• External connectors:
  • 9 pin monitor monochrome
  • 4x RS 232 [2x on video board, 2x on main board]
  • 1x parallel port [Centronics compatible]
  • IEEE-488

 

High-res photos, combined from multiple close-ups, with distortions, but good for details: