Editing Computer cooling (section)

==Mainframes and supercomputers==
As electronic computers became larger and more complex, cooling of the active components became a critical factor for reliable operation. Early vacuum-tube computers, with relatively large cabinets, could rely on natural or forced air circulation for cooling. However, solid-state devices were packed much more densely and had lower allowable operating temperatures.

Starting in 1965, [[IBM]] and other manufacturers of mainframe computers sponsored intensive research into the physics of cooling densely packed integrated circuits. Many air and liquid cooling systems were devised and investigated, using methods such as natural and forced convection, direct air impingement, direct liquid immersion and forced convection, pool boiling, falling films, flow boiling, and liquid jet impingement. Mathematical analysis was used to predict temperature rises of components for each possible cooling system geometry.<ref name="Sadik94"/>

IBM developed three generations of the Thermal Conduction Module (TCM) which used a water-cooled cold plate in direct thermal contact with integrated circuit packages. Each package had a thermally conductive pin pressed onto it, and helium gas surrounded chips and heat-conducting pins. The design could remove up to 27 watts from a chip and up to 2000 watts per module, while maintaining chip package temperatures of around {{convert|50|°C|abbr=on}}. Systems using TCMs were the [[IBM 3081|3081]] family (1980), [[IBM 3090|ES/3090]] (1984) and some models of the [[IBM ES/9000 family|ES/9000]] (1990).<ref name="Sadik94"/> In the IBM 3081 processor, TCMs allowed up to 2700 watts on a single printed circuit board while maintaining chip temperature at {{convert|69|°C|abbr=on}}.<ref name=DoaneFranzon1993/> Thermal conduction modules using water cooling were also used in mainframe systems manufactured by other companies including Mitsubishi and Fujitsu.

The [[Cray-1]] [[supercomputer]] designed in 1976 had a distinctive cooling system. The machine was only {{convert|77|in|mm}} in height and {{convert|56+1/2|in|mm}} in diameter, and consumed up to 115 kilowatts; this is comparable to the average power consumption of a few dozen Western homes or a medium-sized car. The integrated circuits used in the machine were the fastest available at the time, using [[emitter-coupled logic]]; however, the speed was accompanied by high power consumption compared to later [[CMOS]] devices.

Heat removal was critical. [[Refrigerant]] was circulated through piping embedded in vertical cooling bars in twelve columnar sections of the machine. Each of the 1662 printed circuit modules of the machine had a copper core and was clamped to the cooling bar. The system was designed to maintain the cases of integrated circuits at no more than {{convert|54|°C|abbr=on}}, with refrigerant circulating at {{convert|21|°C|abbr=on}}. Final heat rejection was through a water-cooled condenser.<ref>{{cite book |first=R. M. |last=Russel |chapter=The Cray-1 Computer System |title=Readings in Computer Architecture |publisher=Gulf Professional Publishing |year=2000 |isbn=978-1558605398 |pages=40–42 }}</ref> Piping, heat exchangers, and pumps for the cooling system were arranged in an upholstered bench seat around the outside of the base of the computer. About 20 percent of the machine's weight in operation was refrigerant.<ref>Keith Devlin, ''All the Math That's Fit to Print: Articles from The Guardian'', Cambridge University Press, 1994 {{ISBN|0883855151}} page 146</ref>

In the later Cray-2, with its more densely packed modules, Seymour Cray had trouble effectively cooling the machine using the metal conduction technique with mechanical refrigeration, so he switched to 'liquid immersion' cooling. This method involved filling the chassis of the Cray-2 with a liquid called [[Fluorinert]]. Fluorinert, as its name implies, is an inert liquid that does not interfere with the operation of electronic components. As the components came to operating temperature, the heat would dissipate into the Fluorinert, which was pumped out of the machine to a chilled water heat exchanger.<ref>{{Cite web|url=http://archive.computerhistory.org/resources/text/Cray/Cray.Cray2.1985.102646185.pdf|title=Cray-2 Brochure|access-date=6 October 2012|archive-url=https://web.archive.org/web/20120927165059/http://archive.computerhistory.org/resources/text/Cray/Cray.Cray2.1985.102646185.pdf|archive-date=27 September 2012|url-status=live}}</ref>

[[Performance per watt]] of modern systems has greatly improved; many more computations can be carried out with a given power consumption than was possible with the integrated circuits of the 1980s and 1990s. Recent supercomputer projects such as [[Blue Gene]] rely on air cooling, which reduces cost, complexity, and size of systems compared to liquid cooling.