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The IBM S/390® G4 CMOS system, first shipped in 1997, was the first high-end system to use refrigeration. The decision to employ refrigeration cooling instead of other cooling options such as high-flow air cooling or various water-cooling schemes focused on the potential system performance improvement obtainable by lowering coolant temperatures using a refrigeration system. This paper reviews the historical background of refrigeration from its use in the early 1800s to its implementation in computer systems in the early 1990s. The advantages and disadvantages of using refrigeration in the cooling of computer systems are examined. The advantages have outweighed the disadvantages, leading to the first use by IBM of refrigeration in cooling the S/390 G4 server. The design of the refrigeration system for the S/390 G4 system is described in detail, and some of the key parametric studies that contributed to the final design are described.
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