Stephen Larry Runyon

Design of the IBM RISC System/6000 floating-point execution unit

The IBM RISC System/6000 (RS/6000) floating-point unit (FPU) exemplifies a second-generation RISC CPU architecture and an implementation which greatly increases floating-point performance and accuracy. The key feature of the FPU is a unified floating-point multiply-add-fused unit (MAF) which performs the accumulate operation ({ital A} {times} {ital B}) + {ital C} as an indivisible operation. This single functional unit reduces the latency for chained floating-point operations, as well as rounding errors and chip busing. It also reduces the number of adders/normalizers by combining the addition required for fast multiplication with accumulation. The MAF unit is made practical by a unique fast-shifter, which eases the overlap of multiplication and addition, and a leading-zero/one anticipator, which eases overlap of normalization and addition. The accumulate instruction required by this architecture reduces the instruction path length by combining two instructions into one. Additionally, the RS/6000 FPU is tightly coupled to the rest of the CPU, unlike typical floating-point coprocessor chips.

IBM POWER6 microprocessor physical design and design methodology

The IBM POWER6™ microprocessor is a 790 million-transistor chip that runs at a clock frequency of greater than 4 GHz. The complexity and size of the POWER6 microprocessor, together with its high operating frequency, present a number of significant challenges. This paper describes the physical design and design methodology of the POWER6 processor. Emphasis is placed on aspects of the design methodology, technology, clock distribution, integration, chip analysis, power and performance, random logic macro (RLM), and design data management processes that enabled the design to be completed and the project goals to be met.

Design and implementation of the POWER5/spl trade/ microprocessor

POWER5/sup TM/ is the next generation of IBMs POWER microprocessors. This design, sets a new standard of server performance by incorporating simultaneous multithreading (SMT), an enhanced distributed switch and memory subsystem supporting 164w SMP, and extensive RAS support. First pass hardware using IBMs 130nm silicon-on-insulator technology operates above 1.5GHz at 1.3V. POWER5s dual-threaded SMT creates up to two virtual processors per core, improving execution unit utilization and masking memory latency. Although a simplistic SMT implementation promised /spl sim/20% performance improvement, resizing critical microarchitectural resources almost doubles in many cases the SMT performance benefit at a 24% area. Implementing these microarchitectural enhancements posed challenges in meeting the chips frequency, area, power, and thermal targets.