Hybrid cooling with cycle steering in the IBM eServer z990

Abstract

The IBM eServer™ z990 introduces a new mode for cooling multichip processor modules that enables significantly more processors to be refrigerant-cooled than previously. In recent IBM zSeries® offerings, including G4, G5, G6, and z900, chip junctions in a single multichip module (MCM) located in a central electronic complex (CEC) frame were cooled for reliability and performance benefits, using refrigerant technology, to temperatures lower than those achievable with air cooling. In the z990 system, a hybrid cooling approach is used, allowing refrigeration to be extended to four MCMs in a single CEC, which makes possible denser systems and greater power efficiency compared with prior modular refrigeration technologies used. In the event of a malfunction of the primary refrigeration cooling system, a backup air-cooling system is automatically engaged until the refrigeration problem is fixed. System sensors monitor the cooling state at all times. When air cooling is required, the chip circuit temperatures increase and the logic clocks are optimally adjusted to match the new junction temperatures. When refrigeration cooling is restored, the clocks are adjusted back to their fast speed. This technique allows the z990 system to match the processor density of direct-air-cooled systems while retaining a system performance and reliability benefit from refrigeration.