Intel's Core 2 Extreme & Core 2 Duo: The Empire Strikes Back
by Anand Lal Shimpi on July 14, 2006 12:00 AM EST- Posted in
- CPUs
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.
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Kougar - Friday, July 14, 2006 - link
I wasn't sure of the B2 Stepping 6 info because it has been impossible to find CPU-Z shots of this chip, let alone anyone reviewing them!!Mostly I just want to ensure Intel doesn't pull any surprises or OC limiting with them, at this point if the B2 Stepping 6 with that last round of bugfixing performs even the same as a Stepping 5 I'd be extremely happy!
redpriest_ - Friday, July 14, 2006 - link
Thanks Wesley - my Core 2 Duo Extreme X6800 is definitely a Stepping 6, Revision B2 Conroe. It has a packaging date of July 5, 2006. I have all the multipliers unlocked, and I am stuck at around 3.466 ghz using multipliers only for stability. I am running on the Intel 975X BadAxe rev 304 with the latest BIOS.I haven't tried upping the bus from there, yet - I am using 1.4 volts; default voltage isn't dual prime 95 stable at 3.466 ghz, but is at 3.2 ghz.
I haven't tried any intermediate voltages between there to test, so it's possible my Conroe is stable at 3.466 ghz at less voltage. I'll give that a try.
Kougar - Friday, July 14, 2006 - link
What motherboard is this? Have you double-checked your RAM settings and memory ratio? I'd imagine setting a 1:1 ratio, using the most relaxed timings, and slowly ramping up the FSB would get you further. And do try less voltages... ;)That's my plan anyway, DDR2-800 memory speeds on a 1:1 ratio thanks to a 400FSB, 10x multiplier... :)
Kougar - Friday, July 14, 2006 - link
Anandtech used Engineering Sample CPUs, so they would be B0 Stepping 4 or B1 Stepping 5 only. Only retail models will be B2 stepping 6...Did you change your cpu voltage any? Sounds like you didn't ;)
redpriest_ - Friday, July 14, 2006 - link
I had to - 1.4 (1.35 real) to get to 3.466, and 1.5 to 3.733.Wesley Fink - Friday, July 14, 2006 - link
Did you OC by adjusting multipliers first? We could run the X6800 at 3.46 at 13 multiplier using stock voltage, but using 315 bus times the stock 11 multiplier required a small voltage increase. The easiest OCs used higher multipliers and modest FSB increases. The E Conroes are locked, however, and can only be overclocked by increasing the FSB.redpriest_ - Friday, July 14, 2006 - link
Yes, I tried using multipliers only, I haven't fiddled with bus speed yet.Kougar - Friday, July 14, 2006 - link
First, the X6800 is selling at NewEgg, and they are price gouging it for all it's worth. Still listed in stock after having been up for 3+ hours...What a great way to start the day... Thank you Anandtech for this great article! Supurb! Now I have to agree with the poster above me, some info on the E6300 overclocking would about round out my curiosity!
I have a question though, do y'all or anyone else have some CPUZ shots of a retail shipping Conroe? I believe this are supposed to be revision B2 stepping 6??
As for the expected skeptics, my saying the numbers appear to jive won't mean anything... so I'll just say there are over 25 reviews out now of the Core 2 Duo released today. :)
mAdMaLuDaWg - Friday, July 14, 2006 - link
I'm curious on if you tried OCing the E6300. What was the highest stable speed you were able to get.xsilver - Monday, July 17, 2006 - link
for those who dont want to read the xbit labs articlethe overclocking of the e6300 is limited by the motherboard - eg. cant get the board to boot at any higher than 420mhz fsb
we may have to wait for nvidia's core2 solution to see higher fsb's