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An Overview

Larrabee: Intel's New GPU
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The first thing that needs to be pointed out about Larrabee is that it’s not like other GPUs. In fact, it’s not really a GPU at all. As the diagram shows, Larrabee is really a group of several very simple x86 processors, executing instructions in order, and extended with a vector floating point unit (FPU) operating on 512-bit vectors (16 single precision floating-point numbers/integers or eight double-precision floating-point numbers). Each core has 256 KB of cache memory, and communication between processors and cache coherence is handled by a ring bus. The only components that suggest this isn’t just a highly-parallel CPU like the Cell are the texture units and the display interface.

The Cores In Detail: Something New and Something (Very) Old

Like IBM with its Cell architecture, Intel made the following observation: the most demanding applications for processing power generally have a very linear flow of instructions. There are few branchings and dependencies between instructions, so consequently, modern processors, which devote a large part of their total die area to control logic (branch prediction and dynamic instruction scheduling), are not really suited for this type of task.

For an equal number of transistors, rather than following the usual design track by integrating two or four of these “big” processors on a die, it makes much more sense for tasks like this to use a large number of small, much simpler processors. Intel has issued a comparative table justifying its choice:

As the chart shows, for an equal die area and comparable power consumption, the in-order cores (not identical to the ones Larrabee uses) offer a vector instruction throughput 20 times greater than a Core 2 Duo at the same clock frequency. Having made that choice, it was time to design the new processors themselves. The choice of the instruction set was really no choice at all. Since Larrabee was to be Intel’s Trojan horse, with which it would enter the discrete GPU world using its x86 architecture, the architecture for the instruction set was already a known quantity.

Still the choice can seem surprising, since the x86 instruction set is complex (with its CISC architecture) and its support of all the instructions that have been added over the course of its history has an impact on the number of transistors needed compared to RISC architectures.

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  • 0 Hide
    thepinkpanther , March 23, 2009 6:35 AM
    very interesting, i know nvidia cant settle for being the second best. As always its good for the consumer.
  • 6 Hide
    IzzyCraft , March 23, 2009 6:49 AM
    Yes interesting, but intel already makes like 50% of every gpu i rather not see them take more market share and push nvidia and amd out although i doubt it unless they can make a real performer, which i have no doubt on paper they can but with drivers etc i doubt it.
  • 0 Hide
    Anonymous , March 23, 2009 6:50 AM
    I wonder if their aim is to compete to appeal to the gamer market to run high end games?
  • 0 Hide
    Alien_959 , March 23, 2009 8:12 AM
    Very interesting, finally some more information about Intel upcoming "GPU".
    But as I sad before here if the drivers aren't good, even the best hardware design is for nothing. I hope Intel invests more on to the software side of things and will be nice to have a third player.
  • 0 Hide
    crisisavatar , March 23, 2009 8:28 AM
    cool ill wait for windows 7 for my next build and hope to see some directx 11 and openGL3 support by then.
  • 0 Hide
    Stardude82 , March 23, 2009 8:32 AM
    Maybe there is more than a little commonality with the Atom CPUs: in-order execution, hyper threading, low power/small foot print.

    Does the duo-core NV330 have the same sort of ring architecture?
  • 2 Hide
    liemfukliang , March 23, 2009 10:27 AM
    Driver. If Intel made driver as bad as Intel Extreme than event if Intel can make faster and cheaper GPU it will be useless.
  • 3 Hide
    IzzyCraft , March 23, 2009 10:44 AM
    Hope for an Omega Drivers equivalent lol?
  • 1 Hide
    phantom93 , March 23, 2009 11:16 AM
    Damn, hoped there would be some pictures :( . Looks interesting, I didn't read the full article but I hope it is cheaper so some of my friends with reg desktps can join in some Orginal Hardcore PC Gaming XD.
  • 9 Hide
    Slobogob , March 23, 2009 11:51 AM
    I was quite suprised by the quality of this article and am quite eager to see the follow up.
  • 1 Hide
    JeanLuc , March 23, 2009 12:26 PM
    Well I am looking forward to Larrabee but I'll keep my optimisim under wraps until I start seeing some screenshots of Larabee in action playing real games i.e. not Intel demo's.

    I wonder just how compatible larrabee is going to be with older games?
  • 3 Hide
    tipoo , March 23, 2009 12:46 PM
    Great article! Keep ones like this coming!
  • -2 Hide
    tipoo , March 23, 2009 12:48 PM
    IzzyCraftHope for an Omega Drivers equivalent lol?



    That would be FANTASTIC! Maybe the same people who make the Omega drivers could make alternate Larrabee drivers? We all know Intel sucks balls at drivers.
  • 7 Hide
    armistitiu , March 23, 2009 12:49 PM
    So this is Intel's approach to a GPU... we put lots of simple x86 cores in it , add SMT and vector operations and hope that they would do the job of a GPU. IMHO Larrabee will be a complete failure as GPU but as an x86 CPU that is highly parallel this thing could screw AMD's FireStream and NVIDIA's CUDA (OPENCL too) beacause it's x86 and the programming is pretty popular for this kind of architecture.
  • 0 Hide
    wicko , March 23, 2009 1:18 PM
    IzzyCraftYes interesting, but intel already makes like 50% of every gpu i rather not see them take more market share and push nvidia and amd out although i doubt it unless they can make a real performer, which i have no doubt on paper they can but with drivers etc i doubt it.

    Yeah but that 50% includes all the integrated cards that no consumer even realizes they're buying most of the time.. but not in discrete cards. I'd like to see a bit more competition on the discrete side.
  • 2 Hide
    B-Unit , March 23, 2009 1:26 PM
    wtfnl"Simultaneous Multithreading (SMT). This technology has just made a comeback in Intel architectures with the Core i7, and is built into the Larrabee processors." just thought i'd point out that with the current amd vs intel fight..if intel takes away the x86 licence amd will take its multithreading and ht tech back leaving intel without a cpu and a useless gpu


    Umm, what makes you think that AMD pioneered multi-threading? And Intel doesnt use HyperTransport, so they cant take it away.
  • 1 Hide
    justaguy , March 23, 2009 2:02 PM
    Now we know what they're trying to do with it. There's still no indication if it will work or not.

    I really don't see the 1st gen. being successful-it's not like AMD and nVidia are goofing around waiting for Intel to join up and show them a real GPU. Although there's no numbers on this that I've seen, I'm thinking Larry's going to have a pretty big die size to fit all those mini-cores so it better perform, because it will cost a decent sum.
  • 8 Hide
    crockdaddy , March 23, 2009 2:09 PM
    I would mention ... "but will it play crysis" but I am not sure how funny that is anymore.
  • -4 Hide
    Pei-chen , March 23, 2009 2:12 PM
    Can't wait for Larrabee; hopefully a single Larrabee can have the performance of 295. Nvidia and ATI are slacking as they know they can price fixing and stop coming out with better GPU, just more cards with the same old GPU.
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