Bruce C. Giamei

IBM's S/390 G5 microprocessor design

The IBM S/390 G5 microprocessor in IBMs newest CMOS mainframe system provides more than twice the performance of the previous generation, the G4. The G5 system offers improved reliability and availability, along with new architectural features such as support for IEEE floating-point arithmetic and a redesigned L2 cache and processor interconnect. The G5 system implements the ESA/390 instruction-set architecture, which is based on and compatible with the original S/360 architecture. Therefore, it has no RISC (reduced-instruction-set computing) concepts and is one of the most complex of all CISC (complex-instruction-set computing) architectures. Designers had to meet a unique set of challenges to achieve the G5s level of performance-for example, achieving a very high frequency given the complexity of the architecture.