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Cray-2

Overview

The Cray-2, designed by Seymour Cray at Cray Research, was released in 1985 and held the title of world’s fastest supercomputer from 1985 to 1987. With a peak performance of 1.9 GFLOPS and four vector processors, it represented Cray’s first successful multi-processor design (earlier attempts with the CDC 8600 had failed). It was famous for its revolutionary Fluorinert liquid immersion cooling system, which gave the machine a striking visual appearance and earned it the nicknames “Bubbles” and – colloquially – “the world’s most expensive aquarium.”

Key People

  • Seymour Cray – architect and primary designer
  • Cray pursued three simultaneous advances: more functional units, tighter packaging (reducing signal delays), and faster components

Technical Specifications

Parameter Value
Processors 4 custom vector processors
Clock cycle 4.1 nanoseconds (243 MHz)
Peak performance 1.9 GFLOPS
Word size 64 bits
Main memory 256 million words (2 GB) – the first delivery possessed more memory than all previously delivered Cray machines combined
Power consumption 150–200 kW
Weight 5500 pounds (2500 kg)
Height 45 inches (114 cm) – mainframe only
Diameter 53 inches (135 cm) – mainframe only
Price $12M–$17M per unit
Units produced 27 (some sources say 25)
Released 1985
Discontinued 1990

Fluorinert Liquid Immersion Cooling

The Cray-2’s most distinctive feature was its cooling system. The dense 3D packaging – eight circuit boards stacked and connected via pogo pins into ~30 mm high modules – generated enormous heat loads that could not be managed by conventional air cooling.

How It Worked

  • The entire processor module assembly was immersed in a tank of Fluorinert, an electrically inert, transparent liquid manufactured by 3M
  • Fluorinert was forced sideways through the modules under pressure at roughly one inch per second
  • Heated liquid was pumped to external chilled-water heat exchangers and returned to the main tank
  • The cooling tower behind the CPU re-circulated the Fluorinert throughout the system

Visual Effect

The transparent Fluorinert tank made the internal circuitry visible, and the flowing liquid created a shimmering, bubble-filled appearance. TIME magazine described the machine as looking “like a cross between a recreation-room bar and an aquarium” with blue-tinted towers “washed by 200 gallons of liquid coolant” that “bubble and shimmer like over-heated Lava Lites.”

The “Aquarium” Jokes

The Cray-2’s aquarium-like appearance inspired widespread humor:

  • The machine was nicknamed “Bubbles”
  • Common jokes included “No Fishing” signs placed on the machine
  • Cardboard depictions of the Loch Ness Monster were placed in or near the cooling tank
  • The machine became colloquially known as “the world’s most expensive aquarium”
  • It was noted that Fluorinert is also used as an artificial blood plasma – an incongruous factoid that added to the machine’s mystique

Design and Construction

The Cray-2 was Seymour Cray’s first successful multi-processor design. The CDC 8600 (an earlier attempt at multiple CPUs) had been abandoned. The Cray-2’s four processors shared the massive 256-megaword memory, enabling parallel computation.

The extreme density of the packaging – with stacked 3D circuit boards and pogo-pin interconnects – was revolutionary but created the thermal challenges that necessitated liquid immersion cooling.

Production and Delivery

Serial Customer Notes
S/N 1 Lawrence Livermore National Laboratory First delivery, May 1985, installed at National Magnetic Fusion Energy Computer Center (NMFECC)
S/N 2101 NERSC 8-processor unit, reportedly the only one ever made
Others Various DOE, DOD, NASA, industry  

Total production: 27 units (some sources say 25), at $12M–$17M each.

Scientific and Military Applications

Primary Users

  • U.S. Department of Energy / Department of Defense: Nuclear weapons research
  • Lawrence Livermore National Laboratory: First customer; nuclear fusion and weapons simulation
  • NASA: Computational fluid dynamics, spacecraft design
  • Ford Motor Company and General Motors: Finite element analysis, crash testing simulations

Oceanographic Research

Used for sonar development and ocean modeling applications.

Weather and Climate

While NCAR’s primary Cray during the 1980s was the Cray-1A and later the Cray X-MP, the Cray-2’s massive memory (256 megawords – unprecedented at the time) made it particularly suited for large-scale climate and physics simulations that were memory-limited on earlier machines.

Performance Context

The Cray-2 was the fastest machine in the world from 1985 until it was surpassed by the Cray Y-MP in 1988 (which offered 2.667 GFLOPS with up to eight processors).

For modern perspective: an iPad 2 (2012) matched the Cray-2’s historical LINPACK performance on embedded benchmarks.

Notable Anecdotes

  • The Fluorinert cooling system made the Cray-2 visually unlike any other computer before or after. Visitors were mesmerized by the shimmering liquid and visible circuit boards.
  • “No Fishing” signs and Loch Ness Monster cutouts became standard decorations at Cray-2 installations.
  • The 256-megaword memory of the first delivery exceeded the combined memory of every Cray machine previously shipped – a staggering leap.
  • Fluorinert’s dual use as artificial blood plasma was a popular conversation starter at installations.
  • At $17M (the high end), the Cray-2 cost roughly $17 per KFLOPS – expensive by later standards, but revolutionary for 1985.

Successor

The Cray-2 was succeeded by the Cray Y-MP (1988). Its spiritual successor was the Cray X1. Seymour Cray went on to design the Cray-3, which used gallium arsenide chips, but only one production unit was completed.

Current Status

Several Cray-2 units survive in museum collections:

  • Computer History Museum, Mountain View, CA
  • National Cryptologic Museum, Fort Meade, MD
  • Various other institutions and private collections

The Fluorinert cooling tanks no longer contain liquid in museum displays, but the distinctive design remains immediately recognizable.

Sources