Commodore 900
Also known asC900, Z-8000, Z-Machine
Units shippedFifty prototypes built
Media1.2 MB 5.25" floppy disks[1]
Operating systemCoherent
CPUZilog Z8001 @ 10 MHz[1]
Memory512 KB RAM[1]
Storage20 MB hard drive[1]
GraphicsMOS Technology 8563
PredecessorCommodore PET

The Commodore 900 (also known as the C900, Z-8000, and Z-Machine)[2][3] was a prototype microcomputer originally intended for business computing and, later, as an affordable UNIX workstation.[4][5][6] It was to replace the aging PET/CBM families of personal computers that had found success in Europe as business machines. The project was initiated in 1983 by Commodore systems engineers Frank W. Hughes, Robert Russell, and Shiraz Shivji.[7]

In early 1983, Commodore announced an agreement with Zilog to adopt the Z8000 family of processors for its next generation of computers, conferring rights to Commodore to manufacture these processors and for Zilog to manufacture various Commodore-designed integrated circuit products. Zilog was to manufacture components for Commodore's computers, allowing Commodore to expand its own semiconductor operation.[8] Commodore had reportedly been developing its own 16-bit microprocessor, abandoning this effort to adopt the Z8000.[9]


The C900 was a 16-bit computer based on the segmented version of the Zilog Z8000 CPU.[10] Initial announcements indicated the use of a 10 MHz Z8001 processor,[1] but earlier technical documentation suggested the use of a 6 MHz part and detailed the option of a Z8070 arithmetic processing unit (APU) running at 24 MHz.[3] The specification as announced in 1984 featured 256 KB of RAM and a 10 MB hard drive,[11] but subsequently settled on 512 KB of RAM and a 20 MB hard drive as the minimum configuration, with 40 MB and 67 MB hard drives offered as options.[4] A minimum configuration system had been expected to provide only 128 KB of RAM and a 320 KB floppy drive, selling for under $1,000.[12]

Two versions of the machine were developed: a workstation with 1024 × 800 pixel graphics and a multi-user system featuring a text-only display intended to act as a server for a number of connected character-based terminals.[10][4] For the text-only configuration and for lower-resolution graphical output, the system employed the MOS Technology 8563 video controller,[13] this supporting an 80 × 25 colour textual display or a 600 × 400 colour graphical display.[3] The high-resolution display option employed 128 KB of dedicated video memory and featured hardware support for blitting operations, this being employed by a graphical environment featuring "multiple overlapping windows".[4]

The C900 ran Coherent, a UNIX-like operating system,[4] claimed in publicity as being "fully compatible with AT&T's Unix System V, version 5.2",[1][14] although the Coherent system was generally regarded as merely providing a level of compatibility with Version 7 Unix.[15] Some observers found the choice of an earlier form of Unix "surprising" given the availability of more recent versions and of Zilog's commitment among other manufacturers to promote System V as the industry standard for Unix.[11] Onyx Systems, a pioneer of Z8000-based systems running Unix, had previously delivered ports of Version 7 Unix[16] and Unix System III for their computers.[17]

Manufacturing of the system was to commence in 1985 at Commodore International's West Germany plant, with availability in the United States announced for the third quarter of the same year, and with pricing starting from approximately $2,700.[14] The machine was publicly demonstrated for the first time outside the US at the 1985 Hanover Fair, with interest in the product described as "overwhelming".[18] Ultimately, only fifty prototypes were made and sold as development systems before the project was cancelled.

The C900's case is similar to the Amiga 2000's but slightly larger.

See also


  1. ^ a b c d e f LeBold, Diane (September 1985). "Commodore Announces Unix®-Compatible Business System". Commodore Microcomputers. Vol. 6, no. 37. Contemporary Marketing, Inc. p. 10. ISBN 0-88731-047-8. ISSN 0744-8724. Retrieved 2020-10-16.
  2. ^ "Commodore 900: The Unix-like workstation/server that was eclipsed by Amiga –". 21 September 2019. Retrieved 2022-12-14.
  3. ^ a b c Frank Hughes (1985-03-01). Commodore c900 Hardware Spec.
  4. ^ a b c d e "Commodore Info Page - Brochures: Commodore 900 [en]". Retrieved 2022-12-14.
  5. ^ Mini-micro Systems. Cahners Publishing Company. 1985.
  6. ^ Predicasts Technology Update. Predicasts. 1985.
  7. ^ Bagnall, Brian (2006). On the Edge: The Spectacular Rise and Fall of Commodore, Variant Press. Page 434. ISBN 0-9738649-0-7
  8. ^ "Commodore to Use Z8000 Family in Its Micros". Computerworld. 24 January 1983. p. 77. Retrieved 10 March 2023.
  9. ^ Libes, Sol (March 1983). "16-Bit Version of 6502 Announced". Computers & Electronics. p. 32. Retrieved 10 March 2023.
  10. ^ a b "Commodore 900 Computer : This is Z Page". Retrieved 2022-12-14.
  11. ^ a b "Hanover 1984". Commodore User. May 1984. pp. 4–5. Retrieved 28 February 2023.
  12. ^ Libes, Sol (March 1983). "Rumors & Gossip". Computers & Electronics. p. 32. Retrieved 10 March 2023.
  13. ^ "Secret Weapons of Commodore: The CBM 900". Retrieved 2022-12-14.
  14. ^ a b "Commodore high-performance micros out". Computerworld. International Data Group. 6 May 1985. p. 57.
  15. ^ Rochkind, Marc J. (November 1985). "Pick, Coherent and THEOS". Byte. pp. 231–239. Retrieved 28 February 2023. Coherent appears to be nearly a clone of UNIX Version 7, an older release of UNIX that has since been replaced by System III and System V. I write "appears to be" because the Coherent manual doesn't say it is based on UNIX.
  16. ^ Onyx C8002 Computer System. Onyx Systems Incorporated. p. 8.
  17. ^ C5002A, C8002A Series Product Description. Onyx Systems Inc. February 1983. Retrieved 3 March 2023.
  18. ^ "Commodore at the Hanover Fair". Commodore International. Vol. 3, no. 2. Fall 1985. p. 10. Retrieved 25 February 2024.