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Blue Gene/L compute chip: Memory and Ethernet subsystem

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13 Author(s)
Ohmacht, M. ; IBM Research Division, Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598, USA ; Bergamaschi, R.A. ; Bhattacharya, S. ; Gara, A.
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The Blue Gene®/L compute chip is a dual-processor system-on-a-chip capable of delivering an arithmetic peak performance of 5.6 gigaflops. To match the memory speed to the high compute performance, the system implements an aggressive three-level on-chip cache hierarchy. The implemented hierarchy offers high bandwidth and integrated prefetching on cache hierarchy levels 2 and 3 (L2 and L3) to reduce memory access time. A Gigabit Ethernet interface driven by direct memory access (DMA) is integrated in the cache hierarchy, requiring only an external physical link layer chip to connect to the media. The integrated L3 cache stores a total of 4 MB of data, using multibank embedded dynamic random access memory (DRAM). The 1,024-bit-wide data port of the embedded DRAM provides 22.4 GB/s bandwidth to serve the speculative prefetching demands of the two processor cores and the Gigabit Ethernet DMA engine. To reduce hardware overhead due to cache coherence intervention requests, memory coherence is maintained by software. This is particularly efficient for regular highly parallel applications with partitionable working sets. The system further integrates an on-chip double-data-rate (DDR) DRAM controller for direct attachment of main memory modules to optimize overall memory performance and cost. For booting the system and low-latency interprocessor communication and synchronization, a 16-KB static random access memory (SRAM) and hardware locks have been added to the design.

Note: The Institute of Electrical and Electronics Engineers, Incorporated is distributing this Article with permission of the International Business Machines Corporation (IBM) who is the exclusive owner. The recipient of this Article may not assign, sublicense, lease, rent or otherwise transfer, reproduce, prepare derivative works, publicly display or perform, or distribute the Article.  

Published in:

IBM Journal of Research and Development  (Volume:49 ,  Issue: 2.3 )