A HIGH-FREQUENCY CUSTOM CMOS S 390 MICROPROCESSOR/

The S/390(R) Parallel Enterprise Server Generation 4 processor is an i mplementation of the IBM ESA/390(TM) architecture on a single custom C MOS chip. It was designed on a blank slate after consideration of rema pping either a prior CMOS design or a prior bipolar design. It uses a straightforward pipeline both to achieve a fast cycle time and to spee d the design cycle. The complex instructions are implemented using hig hly privileged subroutines called millicode. To achieve high data inte grity while maintaining a high clock frequency, the chip contains dupl icate I-and E-units which perform the same operations each cycle and h ave their results compared.