You have already seen that the Core 2 Extreme X6800 outperforms AMD's fastest processor, the FX-62, by a wide margin.  This is exacerbated by the fact that the $316 E6600, running at 2.4GHz, outperforms the FX-62 in almost every benchmark we ran.  That certainly address the questions of raw performance and value.

For most enthusiasts, however, there is also the important question of how Core 2 processors overclock.  As AMD has moved closer to the 90nm wall, recent AM2 processors do not have much headroom.  A prime example is the FX-62, which is rated at 2.8GHz, reaches 3GHz with ease, but then has a difficult time reaching or passing 3.1GHz on air.  So how does Core 2, built at 65nm, compare in overclocking?

The top X6800 is rated to run at 11X multiplier on a 1066MHz FSB; it is the only Core 2, however, that is completely unlocked, both up and down.  You can adjust multipliers up to 60 on the Asus P5W-DH motherboard, or down to 6.  This makes the X6800 an ideal CPU for overclocking, even though top-line processors are normally notorious for not being the best overclockers.

To gauge the overhead or overclocking abilities of the X6800 in the simplest terms, the CPU speed was increased, keeping the CPU voltage at the default setting of 1.20V.

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At default voltage the X6800 reached a stable 3.6GHz (13 x277).  This is a 23% overclock from the stock 2.93GHz speed at stock voltage.  It is also an important overclocking result, since it implies Intel could easily release a 3.46GHz or 3.6GHz Core 2 processor tomorrow if they chose to.  It is clear there is no need for these faster Core 2s yet, but it does illustrate the speed range possible with the current Core 2 Duo architecture.

The X6800 was then pushed to the highest CPU speed we could achieve with Air Cooling.  We did use a very popular and effective air cooler for our testing, the Tuniq Tower.

The goal was to reach the highest possible speed that was benchmark stable.  Super Pi, 3DMarks, and several game benchmarks were run to test stability. The 2.93GHz chip reached 4.0GHz on air cooling in these overclocking tests.  That represents a 36% overclock on air with what will likely be the least overclockable Core 2 processor - the top line X6800.

To provide some idea of overclocking abilities with other Core 2 Duo processors, we ran quick tests with E6700 (2.67GHz), and E6600 (2.4GHz).  The test E6700 reached a stable 3.4GHz at default voltage and topped out at 3.9GHz with the Tuniq Cooler.  The 2.4GHz E6600 turned out to be quite an overclocker in our tests.  Even though it was hard-locked at a 9 multiplier it reached an amazing 4GHz in the overclocking tests.  That represents a 67% overclock. 

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We had another Core 2 Extreme X6800 that we tried overclocking with a stock Intel HSF. The results were not as impressive as with the Tuniq cooler, with 3.4GHz being the most stable we could get it. We're going to be playing around with these processors more in the future to hopefully get a better overall characterization of what you can expect.

Curious about our overclocking successes, we asked Intel why Core 2 CPUs are able to overclock close to the same levels as NetBurst processors can, despite having less than half the pipeline length. Intel gave us the following explanation:

NetBurst microarchitecture is constrained by physical power / thermal limitations long before the constraint of pipeline stages comes into play. The microarchitecture itself would continue to scale upwards if not for the power constraints. (In fact, we have seen Presler overclocked to 6 GHz in liquid nitrogen environments. At that level, power delivery through the power supply & board itself begin to limit further scaling of the processor.)

Intel's explanation makes a great deal of sense, especially when you remember the original claims that NetBurst was supposed to be good for between 5GHz - 10GHz. NetBurst never got the chance to reach its true overclocking prime as Intel hit thermal density walls well before the 5GHz - 10GHz range and thus Intel's Core architecture was born. Intel's Core 2 processors once again give us an example of the good ol' days of Intel overclocking, where moving to a smaller manufacturing process meant we'd have some highly overclockable chips on our hands. With NetBurst dead and buried, the golden age of overclocking is back.

Enthusuasts have not seen overclocking like this since Socket 478 days, and in fact Core 2 may be even better.  The 2.4GHz E6600, which outperformed the FX-62 in most benchmarks at stock speed costs $316, and overclocked to 4Ghz with excellent air cooling.  With that kind of performance, value, and overclocking the E6600 will likely become the preferred chip for serious overclockers - particularly those that are looking for champagne performance on a smaller budget.

It is important, however, not to sell the advantages of the X6800 short.  AnandTech never recommends the fastest chip you can buy as a good value choice, but X6800 does bring some advantages to the table.  It is the only Conroe that is completely unlocked.  This allows settings like 266(stock FSB)x15 for 4.0GHz, settings that keep other components in the system at stock speed.  This can only be achieved with the X6800 - other Core 2 Duo chips are hard-locked - and for some that feature will justify buying an X6800 at $999.  For the rest of us overclockers E6600 is shaping up to be the chip to buy for overclocking.

CPU Bound Gaming Performance Final Words


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  • ianwhthse - Friday, July 14, 2006 - link

    Hmm... some more investigating.

    Firefox leaves space for the images, so I right-clicked and sure enough, I've got a link. "View Image" to look at a single .png, and I get a white blank screen (properties of this particular image says 446px by 654px, 0.04kb in size).
  • JarredWalton - Friday, July 14, 2006 - link

    I'm using Firefox without trouble. Possibly some firewall setting is getting in the way? We had a few brief issues earlier tonight, but that only lasted a few minutes (and we're not sure what happened). If IE and FF both lack images, it sounds like something outside of browser. One note is that I think our image server (images.anandtech.com) blocks access to images if you don't allow the referring URL to be passed along. Meaning, if you were to get the URL of an image and paste that directly into a browser, the image would show up as a 1x1 blank file. Not sure if that affects the graphs as well or not. Reply
  • ianwhthse - Friday, July 14, 2006 - link

    It was the referer info being blocked that was doing it, kinda annoying. Thanks a million. Reply
  • JarredWalton - Friday, July 14, 2006 - link

    Norton is the devil, I swear. They were great when Peter Norton was actually involved, but now it's just a name, and every release gets worse IMO. Norton Internet Security 2002 (2001?) was good; 2003 became a bit worse. 2005 was garbage and I never tried it again. I don't even run software firewall/anti-virus anymore. I've got a hardware firewall, surf with Firefox, password protect my PCs, and don't open stupid email messages. That only works because I'm the only one on the network/PCs, of course. :) Reply
  • ianwhthse - Friday, July 14, 2006 - link

    Yeah, I run an old corporate edition from maybe 2001-2002 because I can't stand the fat of the newer releases. And it's just worked well for me otherwise, I've got a newer edition sitting around in some pile of disks in some closet, but I tried it, hated it, went back.

    I've got a hardware firewall, software firewall, AV, surf w/Firefox, anti-Spyware, AND try not to do anything stupid -- I got'cha beat =P
  • ianwhthse - Friday, July 14, 2006 - link


    I see all the ads on the page (newegg, zipzoomfly, thermaltake, crucial, etc.) that seem to be flash. I also see the images for the header of the page (the Anandtech logo at the top of the page), but it's just the images in the review that are invisible.

    Hmm... I told the firewall (Norton) to lower my protection, and nothing [either browser]. I'll give it a stab disabled.

    *sign* Okay, charts worked w/o Norton running... (even on minimum protection, they wouldn't come up). I guess I'm off to delve into what setting is going to be doing that.
  • Gary Key - Friday, July 14, 2006 - link

    If you are using Opera 9 or 8, did you turn on "refferer" logging under tools - quick preferences or the advanced - network option?
  • xFlankerx - Friday, July 14, 2006 - link

    Excellent article, by far the most detailed released yet. Yea, the E6400 was a rather important part since it's supposed to be equal to AMD's flagship FX-62, but its easy enough to figure out how it would perform from the other processors' performance.

    As for Conroe availability; 25% of Intel's total output should be more than enough. 20% of Intel's manufacturing capacity equals 100% of AMD's. If there is no shortage of AMD processors, 25% of Intel's total output should be more than enough to supply the market with enough processors?

    DigiTimes also reported that Intel will be charging everyone roughly the same price for the processors. Dell might not get the processors for half-off after all.

    That said, these processors are amazing. By far the greatest thing since the Athlon 64 almost 5 years ago. Fun stuff.
  • mikaela - Tuesday, March 16, 2010 - link

    yes, well-written. i also love the images provided here. thanks i can use the info here to write my essay college essay requirements Reply
  • Suraj - Friday, October 20, 2006 - link

    Great article. How did they overclock the e6600? Did they use the same parts listed in "The test" ? Reply

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