An earlier family of S/390 (System/390) mainframes from IBM that were air cooled and used CMOS-based microprocessor technology (a CPU on one chip). Introduced in 1994 as the 9672 series, Parallel Enterprise Servers rapidly replaced the earlier water-cooled, bipolar machines that were considerably larger and more power hungry.
Parallel Enterprise Servers employed symmetric multiprocessing (SMP) and up to 32 servers could be tied together in a Parallel Sysplex cluster. See IBM mainframes
and Parallel Sysplex
S/390 G4 Model
IBM's air-cooled, CMOS-based mainframes hardly resembled the huge water-cooled, bipolar models. (Image courtesy of IBM.)