FSB Bottlenecks: Is 1333MHz Necessary?

Although all desktop Core 2 processors currently feature a 1066MHz FSB, Intel's first Woodcrest processors (the server version of Conroe) offer 1333MHz FSB support. Intel doesn't currently have a desktop chipset with support for the 1333MHz FSB, but the question we wanted answered was whether or not the faster FSB made a difference.

We took our unlocked Core 2 Extreme X6800 and ran it at 2.66GHz using two different settings: 266MHz x 10 and 333MHz x 8; the former corresponds to a 1066MHz FSB and is the same setting that the E6700 runs at, while the latter uses a 1333MHz FSB. The 1333MHz setting used a slightly faster memory bus (DDR2-811 vs. DDR2-800) but given that the processor is not memory bandwidth limited even at DDR2-667 the difference between memory speeds is negligible.

With Intel pulling in the embargo date of all Core 2 benchmarks we had to cut our investigation a bit short, so we're not able to bring you the full suite of benchmarks here to investigate the impact of FSB frequency. That being said, we chose those that would be most representative of the rest.

Why does this 1333MHz vs. 1066MHz debate even matter? For starters, Core 2 Extreme owners will have the option of choosing since they can always just drop their multiplier and run at a higher FSB without overclocking their CPUs (if they so desire). There's also rumor that Apple's first Core 2 based desktops may end up using Woodcrest and not Conroe, which would mean that the 1333MHz FSB would see the light of day on some desktops sooner rather than later.

The final reason this comparison matters is because in reality, Intel's Core architecture is more data hungry than any previous Intel desktop architecture and thus should, in theory, be dependent on a nice and fast FSB. At the same time, thanks to a well engineered shared L2 cache, FSB traffic has been reduced on Core 2 processors. So which wins the battle: the data hungry 4-issue core or the efficient shared L2 cache? Let's find out.

On average at 2.66GHz, the 1333MHz FSB increases performance by 2.4%, but some applications can see an even larger increase in performance. Under DivX, the performance boost was almost as high as going from a 2MB L2 to a 4MB L2. Also remember that as clock speed goes up, the dependence on a faster FSB will also go up.

Thanks to the shared L2 cache, core to core traffic is no longer benefitted by a faster FSB so the improvements we're seeing here are simply due to how data hungry the new architecture is. With its wider front end and more aggressive pre-fetchers, it's no surprise that the Core 2 processors benefit from the 1333MHz FSB. The benefit will increase even more as the first quad core desktop CPUs are introduced. The only question that remains is how long before we see CPUs and motherboards with official 1333MHz FSB support?

If Apple does indeed use a 1333MHz Woodcrest for its new line of Intel based Macs, running Windows it may be the first time that an Apple system will be faster out of the box than an equivalently configured, non-overclocked PC. There's an interesting marketing angle.

Memory Latency: No Integrated Memory Controller Necessary Power Consumption: Who is the king?
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  • finbarqs - Friday, July 14, 2006 - link

    just to show you how EASY it is to O/C the system! (and for the Futuremark junkies :-) )

    http://www.futuremark.com/forum/showthread.php?p=1...">http://www.futuremark.com/forum/showthread.php?p=1...

    You would want one :)

    if you want to know, 3DMark 2001SE posted a score of 45k, and 3DMark 2003 posted a 33k, FACTORY.
    Reply
  • phaxmohdem - Friday, July 14, 2006 - link

    I was wondering if you could possibly do some "single core" performance testing in the CPU's by simply changing the HAL to "ACPI Uniprocessor PC" instead of "multiprocessor PC" This would tel windows to only use one of the Core2 Duo cores, and I think would give us a good indication of how it will perform when released. Especially on the 2MB cache models, since I'm guessing the single cores won't bust out the door with a full 4MB.

    Just some food for thought/consideration. I personally would love to see a few tests run this way and compared to some single/dual core A64's.
    Reply
  • JarredWalton - Friday, July 14, 2006 - link

    Conroe-L is so far off that it's really an afterthought. The only reason it's not shipping is that Intel has a ton of Netburst stuff to offload, IMO. At $145, the PD 945 is still interesting in terms of certain computational tasks. (I miss the QMD Folding@Home cores....) Reply
  • fishbits - Friday, July 14, 2006 - link

    I had hoped AMD could gain even more market-share before something like this happened, would rather see the two CPU makers on more even footing. Intel just hit this one out of the park however, if pricing holds and availability is decent. Was looking at upgrading my 3500 (939) to a $300 X2 4600 after the price drop, but now? It looks like I'll probably keep this system and build a new rig around a $300 Intel 6600, which wins over or smokes the 4600 depending on benchmark. I really don't know what AMD can do to keep me in the short term, because I don't know if they can make any money dropping prices as far as it looks like they'll need to go. Reply
  • SpaceRanger - Friday, July 14, 2006 - link

    One thing to consider though, if you decide to go with the C2D 6600, then you will also have to spend $$ on a new Mobo + Memory (since your DDR RAM won't work on the platforms for C2D. Keep that in mind when you're upgrading. Reply
  • fishbits - Saturday, July 15, 2006 - link

    When I said that if I went with Intel I'd keep my current rig and build a new one around the Conroe, didn't it dawn on you that I'd already "considered" the need to get a new mobo, memory, etc? Reply
  • SpaceRanger - Sunday, July 16, 2006 - link

    Holy arrogance.. EXCUSE ME for pointing something out.. Reply
  • epsilonparadox - Friday, July 14, 2006 - link

    Well the loads of money they made when they had the better performing architecture can hopefully keep them doing very well also the Opteron isn't really being challenged and thats really their moneymaker right now. They shouldn't have any problems lowering prices on their desktop chips while keeping the status quo on the Opterons. Reply
  • zsdersw - Saturday, July 15, 2006 - link

    They can't really keep the status quo on the Opterons either. Woodcrest excels (or, at the very least, is equal to the Opteron) in the 1P and 2P server space.. which is a huge chunk of the overall server market. Reply
  • LoneWolf15 - Friday, July 14, 2006 - link

    While I'm sad to see AMD lose the performance crown, I'm not so obtuse as to deny it's happening.

    I'm excited by Intel's newest chip, but I think the results for me will be that I'll buy a faster Athlon 64 X2 when the prices drop (assuming Socket 939 ones become cheaper as well, I don't plan a move to Socket AM2 for some time to come). So Intel's newest chip should benefit even those of us sticking with an AMD system. :)
    Reply

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