In 1986 Tim King left his job at MetaComCo, along with a few other employees, to start Perihelion Software in England. There they started development of a new parallel-processing operating system known as "Helios". At about the same time a colleague started Perihelion (later Perihelion Hardware) to create a new Transputer based workstation that would run Helios.
While at Metacomco, much of the Perihelion Software team had worked with both Atari and Commodore International, producing ST BASIC for the former, and Amiga DOS for the latter. The principals still had contacts with both companies. Commodore had expressed some interest in their new system, and showed demos of it on an add-on card running inside an Amiga 2000. It appears they later lost interest in it.
It was at this point that Atari met with Perihelion and work started on what would eventually become the ATW. It is not entirely clear why Atari produced this product. While parallel computing was certainly an area of intense interest at the time, it seems odd that Atari would choose to sell such a system given that their current machines were known primarily for their low cost.
The machine was first introduced at the November 1987 COMDEX under the name Abaq. It was later learned that this name was in use in Europe, and changed to the uninspiring ATW800. A first run of prototypes was released in May 1988, followed by a production run in May 1989. In total only 350 machines were produced (depending on the source either 50 or 100 of the total were prototypes).
The team in charge of the ATW's video system, "Blossom", would later work on another Atari project, the Atari Jaguar video game console.
The ATW system consisted of three main parts:
Helios was Unix-like, but not Unix. Of particular note was the lack of memory protection, due largely to the lack of an MMU on the transputer. This is not quite the issue it might seem, as the Transputer's stack-based architecture makes an MMU less important. Meanwhile Helios was Unix-like enough that it ran standard Unix utilities, including the X Window System as the machine's GUI. In addition Helios ran on all of the Transputers in a farm at "the same time", which allowed all computing tasks to be fully distributed. Turning off an ATW would not effect the overall system, the tasks would simply move to other processors.
Blossom supported several video modes:
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All of these were connected using the transputer's 20Mbps processor links. The motherboard also contained four slots for additional "farm cards" containing four transputers each, meaning that a fully expanded ATW contained 17 transputers. Each ran at 20MHz (the -20 in the name) which supplied about 10 MIPS each. The bus was also available externally, allowing several ATWs to be connected into one large farm. The motherboard also included a separate slot for one of the INMOS crossbar switches to improve inter-chip networking performance.
While not much by today's standards, in the 1980s this was largely unheard of. Blossom also included a number of high-speed effects (128 megapixel fill rates) and blitter functionality, including the ability to apply up to four masks on a bit-blit operation in a fashion similar to a modern GPU's ability to apply several textures to a 3D object.
One oddity of the ATW is that it appears that the Blossom was responsible for the DRAM refresh, although the Transputer included such hardware internally.
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