POWER5 system microarchitecture

TLDR

POWER5 builds on POWER4, aiming to preserve binary and structural compatibility while scaling to 64 physical processors. The paper presents the IBM POWER5™ chip, a two‑way simultaneous multithreaded dual‑core processor designed for compatibility with POWER4™ and scalability to 64 cores. POWER5 implements a two‑way simultaneous multithreaded dual‑core architecture that supports single‑threaded and multithreaded execution, dynamically balances resources, enforces software‑set thread priority, and uses dynamic power management to reduce consumption without affecting performance. POWER5 outperforms POWER4 in single‑threaded mode at the same clock frequency.

Abstract

This paper describes the implementation of the IBM POWER5™ chip, a two-way simultaneous multithreaded dual-core chip and systems based on it. With a key goal of maintaining both binary and structural compatibility with POWER4™ systems, the POWER5 microprocessor allows system scalability to 64 physical processors. A POWER5 system allows both single-threaded and multithreaded execution modes. In single-threaded execution mode, a POWER5 system allows for higher performance than its predecessor POWER4 system at equivalent frequencies. In multithreaded execution mode, the POWER5 microprocessor implements dynamic resource balancing to ensure that each thread receives its fair share of system resources. Additionally, software-settable thread priority is enforced by the POWER5 hardware. To conserve power, the POWER5 chip implements dynamic power management that allows reduced power consumption without affecting performance.