Editing Commodore 900 (section)

== Design ==

The C900 was a [[16-bit]] computer based on the segmented version of the [[Zilog Z8000]] [[central processing unit|CPU]].<ref name="zimmers_c900">{{Cite web |title=Commodore 900 Computer : This is Z Page |url=http://www.zimmers.net/cbmpics/c900.html |access-date=2022-12-14 |website=www.zimmers.net}}</ref> Initial announcements indicated the use of a 10&nbsp;MHz Z8001 processor,<ref name="microcomputers-sep-oct-85" /> but earlier technical documentation suggested the use of a 6&nbsp;MHz part and detailed the option of a Z8070 [[math co-processor|arithmetic processing unit]] (APU) running at 24&nbsp;MHz.<ref name="hughes1985"/> The specification as announced in 1984 featured 256&nbsp;KB of RAM and a 10&nbsp;MB hard drive,<ref name="commodoreuser198405_hanover">{{ cite magazine | url=https://archive.org/details/Commodore_User_Magazine_Issue_008/page/5/mode/2up | title=Hanover 1984 | magazine=Commodore User | date=May 1984 | access-date=28 February 2023 | pages=4–5 }}</ref> but subsequently settled on 512&nbsp;KB of RAM and a 20&nbsp;MB hard drive as the minimum configuration, with 40&nbsp;MB and 67&nbsp;MB hard drives offered as options.<ref name="commodoreinfo_c900"/> A minimum configuration system had been expected to provide only 128&nbsp;KB of RAM and a 320&nbsp;KB floppy drive, selling for under $1,000.<ref name="computerselectronics198403_rumors">{{ cite magazine | url=https://archive.org/details/ComputersElectronics1984-03/page/n27/mode/1up | title=Rumors & Gossip | magazine=Computers & Electronics | last1=Libes | first1=Sol | date=March 1983 | access-date=10 March 2023 | pages=32 }}</ref>

Two versions of the machine were developed: a [[computer workstation|workstation]] with {{nowrap|1024 × 800}} [[pixel]] graphics and a multi-user system featuring a text-only display intended to act as a [[Server (computing)|server]] for a number of connected [[text mode|character-based]] [[computer terminal|terminals]].<ref name="zimmers_c900" /><ref name="commodoreinfo_c900" /> For the text-only configuration and for lower-resolution graphical output, the system employed the [[MOS Technology 8563]] video controller,<ref>{{Cite web |title=Secret Weapons of Commodore: The CBM 900 |url=http://www.floodgap.com/retrobits/ckb/secret/900.html |access-date=2022-12-14 |website=www.floodgap.com}}</ref> this supporting an {{nowrap|80 × 25}} colour textual display or a {{nowrap|600 × 400}} colour graphical display.<ref name="hughes1985"/> The high-resolution display option employed 128&nbsp;KB of dedicated video memory and featured hardware support for [[Bit blit|blitting]] operations, this being employed by a graphical environment featuring "[[windowing system|multiple overlapping windows]]".<ref name="commodoreinfo_c900" />

The C900 ran [[Coherent (operating system)|Coherent]], a [[UNIX-like]] [[operating system]],<ref name="commodoreinfo_c900" /> claimed in publicity as being "fully compatible with [[AT&T]]'s [[Unix System V]], version 5.2",<ref name="microcomputers-sep-oct-85"/><ref name="computerworld19850506_commodore"/> although the Coherent system was generally regarded as merely providing a level of compatibility with [[Version 7 Unix]].<ref name="byte198511_rochkind">{{ cite magazine | url=https://archive.org/details/byte-magazine-1985-11/page/n234/mode/1up | title=Pick, Coherent and THEOS | magazine=Byte | last1=Rochkind | first1=Marc J. | date=November 1985 | access-date=28 February 2023 | pages=231–239 | quote=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. }}</ref> 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.<ref name="commodoreuser198405_hanover"/> [[Onyx Systems]], a pioneer of Z8000-based systems running Unix, had previously delivered ports of Version 7 Unix<ref name="onyx_c8002">{{ cite book | url=https://archive.org/details/bitsavers_onyxc8002O_7368856/page/n9/mode/2up | title=Onyx C8002 Computer System | publisher=Onyx Systems Incorporated | page=8 }}</ref> and [[Unix System III]] for their computers.<ref name="onyx_c5002a">{{ cite book | url=https://archive.org/details/bitsavers_onyxbrochuProductDescriptionFeb83_2404879/mode/2up | title=C5002A, C8002A Series Product Description | publisher=Onyx Systems Inc. | date=February 1983 | access-date=3 March 2023 }}</ref>

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.<ref name="computerworld19850506_commodore">{{ cite magazine | url=https://archive.org/details/computerworld1918unse/page/57/mode/1up | magazine=Computerworld | publisher=International Data Group | title=Commodore high-performance micros out | date=6 May 1985 |pages=57 | language=en }}</ref> 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".<ref name="commodorenews1985">{{ cite magazine | url=https://archive.org/details/commodore-news-vol-3-num-2-fall-1985/page/10/mode/1up | title=Commodore at the Hanover Fair | magazine=Commodore International | date=Fall 1985 | access-date=25 February 2024 | volume=3 | issue=2 | pages=10 }}</ref> 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.