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Big chip for big boxes: IBM cracks open lid on Power7

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IBM will offer Power7 systems that use an updated SMP clustering technology that's more efficient and delivers something closer to linear scalability than prior Power5 and Power6 machines did at the high end of the IBM AIX and OS/400 server lineup.

IBM plans to scale up Power7-based Power Systems as high as 32 sockets, which is where its Power5 and Power6 generations of Power 595 boxes scaled. The difference is that the Power7 boxes will have four times the cores and eight times the threads.

Specifically, a top-end Power7 server will have 32 sockets and 360GB/sec of SMP bandwidth per chip linking them together into a shared-memory system. That high-end machine - which would logically be called the Power 795, but IBM's naming conventions don't obey logic - would have 256 cores and 1,024 threads in total.

IBM is not talking about clock speeds in particular, but Kalla explained that the top-end Power7 chips will offer more than four times the performance of a Power6 chip, and do so in the same thermal envelope. With all those extra threads and other tweaks, that probably means clock speeds ranging from 3GHz to 4GHz.

To save on energy, IBM has added features in the Power7 chip that allow for cores to be turned off and on dynamically, and to set core frequencies on individual cores independently. The design also allows for threads to be disabled on each core until they are all disabled - some workloads don't care about threads and want more clock speed on a single thread. And there's a turbo mode that allows for a core's clock speed to be ramped up by 10 per cent.

Because IBM's Power chips are used in a variety of different platforms, and because getting good yields on such a large chip is difficult at first, IBM will offer different packaging for the Power7 parts.

For two-socket and four-socket blade and rack servers, Kalla says that IBM will create a single chip organic package that has one memory controller - my guess is that this package will have four cores and some of the eDRAM L3 cache deactivated because it has boogers on it.

Midrange and high-end Power7 servers will use a single-chip glass ceramic package that has both memory controllers activated and could sport four and probably six cores (IBM was not precise on the core count in each package) as well as SMP links for systems up to 32 sockets.

In a twist, future Power7 supercomputers will be getting their own quad-chip multichip module (MCM) package, which puts four Power7 chips and eight activated memory controllers on a single package. This is no doubt the configuration going into the Blue Waters massively parallel supercomputer that IBM is building for the National Center for Supercomputing Applications at the University of Illinois. It looks like two of these 32-core MCMs will be put into each 2U rack server in the Blue Waters system.

The Power7 chip is running in the IBM labs right now supporting its AIX and i operating systems as well as Linux.

IBM is one of the few companies left that makes its own chips and servers that wrap around them, and unless something radical happens, Big Blue will continue to do so into the foreseeable future. ®

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