The Xeon Phi family of co-processors was announced in June, but Intel finally disclosed additional details.The Xeon Phi die is a massive chip: Almost 5 billion transistors using Intel's most advanced 22nm process technology with 3D tri-gate transistors.

A maximum of 62 cores can fit on a single die. Each core is a simple in order x86 CPU (derived from the original Pentium) with a 512-bit SIMD unit. There is a twist though: the core can handle 4 threads simultaneously. Nehalem, Sandy and Ivy Bridge also use SMT, but those cores uses SMT mostly to make better use of their ample execution resources.

In case of the Xeon Phi core, the 4 threads are mostly a way to hide memory latency. In the best case, two threads will execute in parallel. 

Each of these cores is a 64-bit x86 core. However, only 2% of the core logic (excluding the L2-cache) is spent on x86 logic. The SIMD unit does not support MMX, SSE or AVX: the Xeon Phi has its own vector format.

All of the cores are connected together with a bi-directional ring, similar to what's used in the Xeon E7 and the Sandy Bridge EP CPUs.

Eight memory channels (512-bit interface) support up to 8 GB of RAM, and PCIe logic is on chip.

The Xeon Phi Cards


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  • Kevin G - Saturday, November 17, 2012 - link

    That rumor has a grain of truth to it. A slide deck about Larrabee from Intel indicated a socketable version fitting into a quad socket Xeon motherboard. This was while Intel still had consumer plans for Larrabee which have since radically changed.

  • alpha754293 - Wednesday, November 14, 2012 - link

    I don't even know what generally (and publically accessible) programs are available that you would be able to use to do this sort of HPC testing.

    OpenMP code is sort of "easier" to come by. A program that has both an OpenMP and a CUDA version where it's a straight port - I can't even think of one.

    The only one that might be a possiblity would be Ansys 13/14 because they do have some limited static structural/mechanical FEA capabilities that can run on the GPU, but I don't know how you'd be able to force it onto the Xeon Phis.

  • TeXWiller - Wednesday, November 14, 2012 - link

    The next version of OpenMP should have accelerator suppport via the OpenACC scheme. I'd bet that most engineering applications will be able to support most accelerators like Phi, Tesla and APUs in a transparent manner simply through the math libraries, not perhaps in the most optimal but at least in a sufficiently worthwhile way. Reply
  • rad0 - Wednesday, November 14, 2012 - link

    One thing I've yet to understand about the Xeon Phi is: do you get to run anything you want on it, or not?

    Could you run Oracle's JVM (or any other JVM) on it? I know HPC isn't all that interested in Java, but a cheap 60-thread Java machine would be very interesting to play with.

    Can you just ssh into the embedded linux and run anything you want?
  • coder543 - Wednesday, November 14, 2012 - link

    Why Java? A dozen negative adjectives pop into my mind at the mere mention of the word outside of a coffee shop. Reply
  • madmilk - Wednesday, November 14, 2012 - link

    You can probably run Java on it, but it will not run well. Most Java code is application code - very branchy, something the Phi's memory architecture cannot handle well. The JVM certainly will not vectorize code either, so you have all those vector units being wasted.

    This is really much closer to a GPU in terms of the kind of optimizations that must be done for performance, even if the underlying instruction set is x86.
  • Jaybus - Thursday, November 15, 2012 - link

    No, it is much closer to a CPU than a GPU. This is an area where it differs VASTLY from a GPU. In fact, the cores are CPUs. Reply
  • llninja1 - Thursday, November 15, 2012 - link

    According to Tom's Hardware, you can login to the Xeon Phi card and get a command line prompt

    so that implies you can do whatever you want with some finagling. Whether your 60-thread JVM thought would work well or not on this architecture remains to be seen.
  • extide - Wednesday, November 14, 2012 - link

    Do some Folding@Home benchmarks on a Phi if at all possible!

  • tipoo - Wednesday, November 14, 2012 - link

    Like the people in charge of F@H would develop and release a new folding core so that it could run on one of these in the off chance some enthusiast has one of these multi thousand dollar cards and a computer system that can run it?

    Not going to happen. This isn't a general CPU core that any existing software can run on, nor is it aimed at home users.

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