Abstract
The approach taken in BlueGene/L (BG/L) is substantially different. The system is built out of a very large number of nodes, each of which has a relatively modest clock rate. Those nodes present both low power consumption and low cost. The design point of BG/L utilizes IBM PowerPC embedded CMOS processors, embedded DRAM, and system-on-a-chip techniques that allow for integration of all system functions including compute processor, communications processor, 3 cache levels, and multiple high speed interconnection networks with sophisticated routing onto a single ASIC.
Description of Blue Gene
Because of a relatively modest processor cycle time, the memory is close, in terms of cycles, to the processor. This is also advantageous for power consumption, and enables construction of denser packages in which 1024 compute nodes can be placed within a single rack. Integration of the inter-node communications network functions onto the same ASIC as the processors reduces cost, since the need for a separate, high-speed switch is eliminated.
The current design goals of BG/L aim for a scalable supercomputer having up to 65,536 compute nodes and target peak performance of 360 teraFLOPS with extremely cost effective characteristics and low power (~1 MW), cooling (~300 tons) and floor space (<2,500 sq ft) requirements. This peak performance metric is only applicable for applications that can utilize both processors on a node for compute tasks. We anticipate that there will be a large class of problems that will fully utilize one of the two processors in a node with messaging protocol tasks and will therefore not be able to utilize the second processor for computations. For such applications, the target peak performance is 180 teraFLOPS.
The BG/L design philosophy has been influenced by other successful massively parallel machines, including QCDSP at Columbia University. In that machine, thousands of processors are connected to form a multidimensional torus with nearest neighbor connections and simple global functions. Columbia University continues to evolve this architecture with their next generation QCDOC machine [QCDOC], which is being developed in cooperation with IBM research. QCDOC will also use a PowerPC processing core in an earlier technology, a simpler floating point unit, and a simpler nearest neighbor network.
