How Many Cores in a Larrabee?

Initial estimates put Larrabee at somewhere in the 16 to 32-core range, we figured 32-cores would be a sweetspot (not in the least because Intel's charts and graphs showed diminishing returns over 32 cores) but 24-cores would be more likely for an initial product. Intel however shared some data that made us question all of that.

Remember the design experiment? Intel was able to fit a 10-core Larrabee into the space of a Core 2 Duo die. Given the specs of the Core 2 Duo Intel used (4MB L2 cache), it appears to be a 65nm Conroe/Merom based Core 2 Duo - with a 143 mm^2 die size.

At 143 mm^2, Intel could fit 10 Larrabee-like cores so let's double that. Now we're at 286mm^2 (still smaller than GT200 and about the size of AMD's RV770) and 20-cores. Double that once more and we've got 40-cores and have a 572mm^2 die, virtually the same size as NVIDIA's GT200 but on a 65nm process.

The move to 45nm could scale as well as 50%, but chances are we'll see something closer to 60 - 70% of the die size simply by moving to 45nm (which is the node that Larrabee will be built on). Our 40-core Larrabee is now at ~370mm^2 on 45nm. If Intel wanted to push for a NVIDIA-like die size we could easily see a 64-core Larrabee at launch for the high end, with 24 or 32-core versions aiming at the mainstream. Update: One thing we did not consider here is power limitations. So while Intel may be able to produce a 64-core Larrabee with a GT200-like die-size, such a chip may exceed physical power limitations. It's far more likely that we'll see something in the 16 - 32 core range at 45nm due to power constraints rather than die size constraints.

This is all purely speculation but it's a discussion that was worth having publicly.

Putting it all Together - Return of the Ring Bus Cache and Memory Hierarchy: Architected for Low Latency Operation
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  • ocyl - Monday, August 04, 2008 - link

    Larrabee will be shipped when Diablo III is, and it will mark the beginning of the end for DirectX.

    Calling it first here at AnandTech.

    Thanks go to Anand and Derek for the very well written article. You are the ones who keep tech journalism alive.
    Reply
  • erikespo - Monday, August 04, 2008 - link

    "At 143 mm^2, Intel could fit 10 Larrabee-like cores so let's double that. Now we're at 286mm^2 (still smaller than GT200 and about the size of AMD's RV770) and 20-cores. Double that once more and we've got 40-cores and have a 572mm^2 die, virtually the same size as NVIDIA's GT200 but on a 65nm process. "

    this math is way off

    143 mm^2 is 20449mm.. if they fit 10 there that is 2044.9 per core
    286mm^2 is 81796mm.. that is 4X the space so 40 cores in 286^2
    and 572mm^2 is 327184mm is 160 cores..

    double length will double area.. doubling length and width will quadruple area.
    Reply
  • bauerbrazil - Monday, August 04, 2008 - link

    Hahahaha, YOUR math is way off!!!

    Jesus.
    Reply
  • erikespo - Monday, August 04, 2008 - link

    I see where the article and you got your math..
    you both did 143mm^2 / 10 and got 14.3 then divided 286^2 by 14.3 and got 20.. this math is only acting on the one number..

    I know this because the area of 14.3 is 204.49 mm. 10 of those would be 2044.9mm. but the area of 143mm^2 is 20449mm.
    Reply
  • WeaselITB - Monday, August 04, 2008 - link

    Wow ... No.
    143mm^2 is NOT equivalent to 143^2 mm ... Your analysis is flawed.

    If we use your example, 2mm^2 is NOT 2mm x 2mm ... it's actually root(2)mm x root(2)mm ... 4mm^2 is 2mm x 2mm, not 4mm x 4mm (that'd be 16mm).

    Maybe you should examine in depth that Wikipedia article you linked earlier ...

    Thanks,
    -Weasel
    Reply
  • MamiyaOtaru - Monday, August 04, 2008 - link

    143mm^2 is NOT equivalent to 143^2 mm

    ^^THIS

    That's it in a nutshell. mm² doesn't mean you square 143, it refers to Square Millimeters, a unit of area (unlike Millimeters, a unit of distance).

    Revised mspaint illustration: http://img379.imageshack.us/my.php?image=squaremmh...">http://img379.imageshack.us/my.php?image=squaremmh...
    Reply
  • erikespo - Monday, August 04, 2008 - link

    Anandtech Comment Section.. Forever record of my retardedness Reply
  • erikespo - Monday, August 04, 2008 - link

    Dang.. Many apologies..
    got my square area and squared numbers confused..
    Reply
  • WeaselITB - Monday, August 04, 2008 - link

    [quote]4mm^2 is 2mm x 2mm, not 4mm x 4mm (that'd be 16mm).[/quote]

    Dang, that was supposed to read "(that'd be 16mm^2)."

    Thanks,
    -Weasel
    Reply
  • erikespo - Monday, August 04, 2008 - link

    another way to look as it is how man 143mm^2 squares does it take to make up 286mm^2?

    only 2 would only be 143mm x 286mm

    since 10 cores fit into 143 x 143, 20 will fit into 143 x 286mm
    286 x 286 (which is double that of 143 x 286mm) the 286mm^2 would fit 40
    Reply

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