Editing Atari Transputer Workstation (section)

== Overview ==
{{Multiple image
| direction = vertical
| width = 200
| header = System views
| image1 = Atw front.jpg
| caption1 = Front
| image2 = Atw inside.jpg
| caption2 = Inside
| image3 = Atw subsys.jpg
| caption3 = MegaST I/O subsystem
| image4 = Atw blossom.jpg
| caption4 = Blossom board
| image5 = Atw farmcard.jpg
| caption5 = Farmcard
}}
{{More citations needed|section|date=March 2021}}
The Atari Transputer Workstation system consists of three main parts:

# the main motherboard containing a T800-20 Transputer and 4&nbsp;MB of [[random-access memory]] (RAM) (expandable to 16&nbsp;MB)
# a complete miniaturized [[Atari ST|Mega ST]] acting as an [[input/output]] (I/O) processor with 512&nbsp;KB of RAM
# the Blossom video system with 1&nbsp;MB of [[dual-ported RAM]]

All of these are connected using the Transputer's 20&nbsp;Mbit/s processor links. The motherboard contains four slots for added ''farm cards'' containing four Transputers each, meaning that a fully expanded ATW contains 17 Transputers.<ref>{{cite web
|url=https://www.atarimuseum.com/computers/16bits/transputer.html
|title=The Atari ABAQ/ATW800 "Transputer"
|archive-url=https://web.archive.org/web/20210703043237/http://www.atarimuseum.com/computers/16bits/transputer.html
|archive-date=3 July 2021
}}</ref> Each runs at 20&nbsp;MHz (the -20 in the name) which supplied about 10 [[Instructions per second#Millions of instructions per second (MIPS)|MIPS]] each. The bus is available externally, allowing several ATWs to be connected into one large farm. The motherboard includes a separate slot for one of the INMOS crossbar switches to improve inter-chip networking performance.

HeliOS is [[Unix-like]], but not [[Unix]]. It lacks memory protection, due largely to the lack of a [[memory management unit]] (MMU) on the Transputer, although a number of measures are employed to reduce the possibility of programs interfering with each other. For example, when invoking a command pipeline, each program is distributed to its own separate processor, communicating with other programs using pipes that are implemented by hardware links. Where many programs may be deployed on the same processor, these processors will not in general be shared by programs belonging to different users.<ref name="byte198806_transputer">{{cite magazine |last1=Pountain |first1=Dick |date=June 1988 |url=https://archive.org/details/BYTE-1988-06/page/n348/mode/1up |title=A Personal Transputer |magazine=[[Byte (magazine)|Byte]] |access-date=21 February 2024 |pages=303–304, 306, 308}}</ref>

HeliOS is Unix-like enough that it ran standard Unix utilities, including the [[X Window System]] as the machine's [[graphical user interface]] (GUI). HeliOS can run on all of the Transputers in a farm concurrently, which allows all computing tasks to be fully distributed. Powering off an ATW does not affect the overall farm, and the tasks simply move to other processors on other systems.

Blossom supports several video modes:
:mode 0: 1280 by 960 pixels, 16 colors out of a palette of 4096 (including 16 true grayscales, on a monochrome monitor)
:mode 1: 1024 by 768 pixels, 256 colors out of a palette of 16.7 million
:mode 2: 640 by 480 pixels (2 virtual screens), 256 colors out of a palette of 16.7 million
:mode 3: 512 by 480 pixels, 16.7 million colors

Blossom also includes 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 is responsible for the DRAM refresh, although the ATW includes such hardware internally.

The video architecture developed by Perihelion for the ATW formed the basis of a "high resolution video engine" expansion card envisaged for the [[TT030]] workstation, connecting to the machine's VMEbus and supporting direct memory access transfers to and from system RAM.<ref name="atari19890421_ttx">{{cite tech report |url=https://archive.org/details/TT-X_Spec_Apr-21-1989/page/n30/mode/1up |title=Atari TT and TT/X Product Specifications The Design of the TT Computer Series |publisher=Atari Corporation |date=21 April 1989 |access-date=22 February 2024 |pages=24}}</ref>