IBM's Power 575 is still impressive for both its computing speed and also its use of basically a system of water-filled copper pipes to cool down those hot processors. IBM says that means 80 percent less air conditioning and 40 percent less power required than older generations of comparable computing might.
Developed at IBM's Zurich lab, the system actually starts with fairly hot 45C water, running it past the blazingly hot microprocessors to bring them down to a (still toasty) 85C operating temperature, which then heats the incoming water beyond 50C, making it hot enough to be used as waste heat for building warming or municipal use. While water cooling in computing isn't a revolutionary concept, its now considered more cost effective and is being revived by IBM as energy costs for data centers spiral upwards.
Relative reading: The Problem Is Us: U.S. Data Center Growth Spawning Climate Disaster
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