Atari Sierra

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Atari Sierra
Atari Sierra mockup.jpg
The only known image of the Sierra mock-up. It looks similar to the Amiga 1000 but has an attached keyboard and an Atari-style joystick port can be seen on the left.
Also known as Rainbow
Developer Atari
Type 16-bit/32-bit personal computer
Release date Prototype 1983 (1983) - Project Cancelled

Sierra was the code name for a 16-bit/32-bit personal computer designed by Atari's Sunnyvale Research Lab (SRL) starting around 1983. The design included a new GPU known as "Silver and Gold", a powerful sound synthesizer known as AMY, and a new operating system code-named "Eva". The two-chip GPU was collectively known as Rainbow, and the system is sometimes referred to by this name.[a] The CPU had not been chosen, but the Motorola 68000 and Intel 286 were being considered.

Sierra was one of several similar machines being designed at the same time by different departments within Atari, and at external contractors like Amiga. At least three such designs are known to have been worked on. All of them were slowed by corporate indecision about how such a machine would be positioned in the market; as a games machine, home computer or even a workstation. Atari eventually chose Amiga's design, only to have it purchased out from under them by Commodore International.

Sierra was still a paper project when the company was purchased by Jack Tramiel in July 1984 and the majority of SRL was laid off. Only the synthesizer had progressed very far at this point, and was produced in small numbers as the Atari AMY.


Earlier 8-bit designs[edit]

Atari's earlier consoles and computers generally used an off-the-shelf 8-bit central processor with custom chips to improve performance and capabilities. With most designs of the era, graphics, sound and similar tasks would normally be handled by the main CPU, and converted to output using relatively simple analog-to-digital converters. Offloading these duties to the custom chips allowed the CPU in Atari's design to spend less time on housekeeping chores. Atari referred to these chips as co-processors, sharing the main memory to communicate instructions and data. In modern terminology, these would be known as integrated graphics and sound, now a common solution for mainstream offerings.[1]

For this role, the Atari 2600 used an all-in-one support chip known as the TIA to provide graphics and sound support to its stripped down MOS Technology 6502-derivative, the 6507. Due to the high price of computer memory, the TIA was designed to use almost no traditional RAM, which led to both a quirky design as well as surprising programming flexibility. It was some time before programmers learned the knack of "racing the beam", but when they did, 2600 games began to rapidly improve compared to early efforts.[1]

The much more powerful Atari 8-bit family used the same basic design concept, but this time supported by three chips. In addition to a 6502B CPU, ANTIC was responsible for handling background graphics (bitmaps) and character-based output, the C/GTIA provided color and sprite support, and the POKEY provided four-channel sound as well as handing some basic input/output tasks like keyboard handling. This separation of duties allowed each sub-system to be more powerful than the all-in-one TIA, while also greatly reducing programming complexity.[2]


By the early 1980s, a new generation of CPU designs was coming to market with much greater capability than the earlier 8-bit designs. Notable among these were the Intel 8088 and similar designs using 16-bit internals, which initially became available as daughtercards on S-100 bus machines and other platforms as early as the late 1970s.[3] However, a family of even more powerful 32-bit designs were also in the pipeline, notably the Motorola 68000 (m68k) of 1979.

Atari's Sunnyvale Research Lab (SRL),[b] run by Alan Kay and Kristina Hooper Woolsey, was tasked with keeping the company on the leading edge, exploring projects beyond the next fiscal year.[c] They began experimenting with the new 32-bit chips in the early 1980s. By 1983, these efforts had been formalized under the Sierra project. Sierra was, in most ways, an updated implementation of the 8-bit series design concept with dramatically improved hardware at every level. The original design proposal outlines a number of ways the design could be tailored to different markets.[4]

Sierra used a new GPU design known as "Rainbow" that was initially implemented in a pair of VLSI chips known as "Silver" and "Gold"[d] and a new synthesizer chip known as "Amy".[4] Tying all of this together would be a new operating system known as "Eva". At least one design document outlining the entire system exists, referring to the platform as "GUMP", a reference to a character in The Marvelous Land of Oz.[5]

For the CPU, numerous options were explored, including the Intel 80186 and 286, National Semiconductor NS16032, Motorola 68000 and Zilog Z8000.[6] Each of these was compared for its price/performance ratio for a wide variety of machines. The original design documents suggest different Sierra concepts aimed at the home computer market with a price point as low as $300 using a low power CPU, all the way through business machines, student computers and low-end workstations.[4]

Other designs[edit]

Sierra proceeded alongside similar projects within Atari being run by other divisions, including an upscale m68k machine known as Gaza.[7][e] Arguments broke out in Atari's management over how to best position any 32-bit machine, and which approach better served the company's needs. The home computer market was in the midst of a price war that was destroying it, and it was not clear that a high-end machine would address this. The business computing market appeared to be weathering the storm, and the new IBM PC was starting off well in spite of being much less sophisticated than Sierra or Gaza, but Atari had no presence in the business world. Workstations were an emerging niche that the company might be able to sell into, but the market was very new. Management vacillated on which of these markets offered a greater chance of success.[8]

Work on the various Sierra concepts continued through 1983 and into 1984, by which point little progress had been made on the complete design. Several mock-ups of various complexity had been constructed, but no working machines existed. Likewise, little concrete work on the operating system had taken place, and the idea of using a Unix System V port was being considered. Only the Amy chip had made considerable progress by this point; the first version to be fabbed, the AMY-1, was moving into production for late 1984.[9]

At the same time, a team of former Atari engineers now working at a third party design firm led by Jay Miner had been making progress with their new platform, codenamed "Lorraine".[10] Lorraine was also based on the 68000 and generally similar to Sierra and Gaza in almost every design note, which is not surprising given that the teams originally came from the same company. By early 1984, Lorraine was further along in design and essentially ready for production. Atari had already licensed the Lorraine chipset for a games console machine, and the Gaza team was told to drop their efforts and begin work on a desktop computer design using Lorraine, codenamed "Mickey" (semi-officially known as the Atari 1850XLD).[8]

Tramiel takeover[edit]

In July 1984, Jack Tramiel purchased Atari and the company became Atari Corporation. In a desperate measure to restore cash-flow, whole divisions of the company were laid off over a period of a few weeks.[11] This included the vast majority of the SRL staff. The Amy team convinced the Tramiels that their work could be used in other platforms, and their project continued. The rest of the Sierra team were scattered.

As a result, any progress on the Sierra platform ended, as well as progress on Gaza and Mickey. The company's option to use Lorraine for a games console also ended, and Amiga would later sign a deal with Commodore International to produce a machine very similar to Mickey, the Amiga 1000.[12] The Atari ST, Atari Corp's 68k-based machine, would be built with custom chips and off-the-shelf hardware, and was significantly less advanced than Sierra or Mickey.


  1. ^ Some documents suggest "Rainbow" referred to Amy as well, others suggest otherwise.
  2. ^ Sometimes referred to as CRG, for Corporate Research Group.
  3. ^ One SRL employee stated the goal was to plan for the CES after the next one.
  4. ^ Although there are some sources suggesting that Rainbow and Silver/Gold were two different GPU systems, documentation from the era clearly shows the later to be part of Rainbow.
  5. ^ There are numerous claims that Gaza was a dual-m68k machine, but this is unlikely due to the way these chips accessed memory. Comments by the engineers suggest the multiple CPUs are referring to coprocessors in the traditional Atari usage of the term.


External Links[edit]


  1. ^ a b Montfort, Nick; Bogost, Ian (2009). Racing the Beam. MIT Press. 
  2. ^ Crawford, Chris (1982). De Re Atari. Atari Program Exchange. 
  3. ^ Johnson, Herbert R. (2011-10-13). "S-100 and the 8086". 
  4. ^ a b c Morrison 1983.
  5. ^ Goldberg & Vendel 2012, p. 732.
  6. ^ Morrison 1983, pp. 6-7.
  7. ^ Goldberg & Vendel 2012, p. 733.
  8. ^ a b Goldberg & Vendel 2012, p. 737.
  9. ^ AMY 1 Spec (PDF) (Technical report). Atari Semiconductor Group. 18 August 1983. 
  10. ^ Goldberg & Vendel 2012, p. 708.
  11. ^ Goldberg & Vendel 2012, pp. 748-749.
  12. ^ Goldberg & Vendel 2012, pp. 745.


  • Goldberg, Marty; Vendel, Curt (2012). Atari Inc. Business Is Fun. Syzygy Press. ISBN 9780985597405. 
  • Morrison, Jerry (9 February 1983). Proposed Sierra Project Plan (Technical report). Atari.