This book constitutes the refereed proceedings of the 9th Asia-Pacific Computer Systems Architecture Conference, ACSAC 2004, held in Beijing, China in September 2004. The 45 revised full papers presented were carefully reviewed and selected from 154 submissions. The papers are organized in topical sections on cache and memory, reconfigurable and embedded architectures, processor architecture and design, power and energy management, compiler and operating systems issues, application-specific systems, interconnection networks, prediction techniques, parallel architectures and programming, microarchitecture design and evaluation, memory and I/O systems, and others.