CRAY-2 Technology

Technological innovations on the CRAY-2 included the use of liquid immersion cooling and the eight-layer, three-dimensional modules.

Liquid Immersion Cooling

Effective cooling techniques were central to the design of high-speed computational systems. Densely packed components resulted in shorter signal paths, thus contributing to higher speeds. Traditionally, the tradeoff has been lower reliability due to increased operating temperatures, but this was no longer a limitation. The liquid immersion cooling technology used by the CRAY-2 was a breakthrough in the design of cooling systems for large-scale computers. It placed the cooling medium in direct contact with the components to be cooled, thus efficiently reducing and stabilizing the operating temperature and increasing system reliability.

The CRAY-2 mainframe operated in a cabinet filled with a colorless, odorless, inert fluorocarbon fluid. The fluid was nontoxic and nonflammable and has high dielectric (insulating) properties. It also had high thermal stability and outstanding heat transfer properties. The coolant flowed through the module circuit boards at a velocity of one inch per second and was in direct contact with the integrated circuit packages and power supplies.

Liquid Immersion Cooling Characteristics

• The key to densely packed electronics

• "Valveless" cooling system

• 200-gallon closed system

• Room temperature cooling ranges

• Accompanying standpipe and reservoir

• Inert, nontoxic and nonflammable

• High insulant properties

• High thermal stability

• High heat transfer capacity

Module Technology Design

The CRAY-2 hardware was constructed of synchronous networks of binary circuits. These circuits were packaged in 320 pluggable modules, each containing approximately 750 integrated circuit packages. The total integrated circuit population in the system was approximately 240,000 chips, nearly 75,000 of which were memory.

The pluggable modules were three-dimensional structures with an 8 x 8 x 12 array of circuit packages. Eight printed circuit boards formed the module structure. Circuit interconnections were made in all three dimensions within the module. Each module measured 1 x 4 x 8 inches, weighed 2 pounds, consisted of approximately 40% integrated circuits by volume, and consumed 300 to 500 watts of power.

The CRAY-2 Common Memory consisted of 128 memory banks with two million words per bank. Each memory bank occupied a circuit module.

CRAY-2 logic networks were constructed of 16-gate array integrated circuits packaged in three-dimensional structures.