The QPACE project aims to build a prototype supercomputer using IBM PowerXCell 8i processors. The system architecture involves node cards containing a PowerXCell processor and network processor, interconnected using a custom 3D torus network. Each node card provides over 26 teraflops of peak performance and uses liquid cooling. The network processor in each node card handles the high-speed FlexIO interface to the PowerXCell processor and communication within the 3D network topology.