Description
The ATW system consisted of three main parts:
- the main motherboard containing a T800-20 transputer and 4MB of RAM (expandable to 16MB)
- a complete miniaturized Mega ST acting as an I/O processor with 512kB of RAM
- the Blossom video system with 1MB of dual-ported RAM
All of these were connected using the transputer's 20 Mbit/s processor links. The motherboard also contained three slots for additional "farm cards" containing four transputers each, meaning that a fully expanded ATW contained 13 transputers. Each ran at 20 MHz (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.
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 graphical user interface (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 affect the overall farm, the tasks would simply move to other processors on other systems.
Blossom supported several video modes:
- mode 0: 1280 by 960 pixels, 16 grayscales out of a palette of 4096
- mode 1: 1024 by 768 pixels, 256 colours out of a palette of 16.7 million
- mode 2: 640 by 480 pixels (2 virtual screens), 256 colours out of a palette of 16.7 million
- mode 3: 512 by 480 pixels, 16.7 million colours
- mode 4: 1280 by 960 pixels, 16 colours out of a palette of 4096
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 graphics processing unit'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.
Read more about this topic: Atari Transputer Workstation
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