Overclocking: Great When Overvolted, Otherwise...

Back when I asked Intel why anyone would opt for LGA-1366 over LGA-1156 one of the responses I got was: overclocking. The most overclockable CPUs will be LGA-1366 chips.

We tried overclocking three different CPUs: the Core i7 870, Core i7 860 and Core i5 750. We overclocked using two different coolers: the retail low profile HSF and a Thermalright MUX-120 (the heatsink Intel is sending around to reviewers for high performance testing). I'll get one thing out of the way: the retail heatsink pretty much sucks for overclocking:

Intel Core i7 870 Max Overclock (Turbo Disabled)
Intel Retail LGA-1156 Cooler 3.52GHz (160MHz x 22.0)
Thermalright MUX-120 4.20GHz (200MHz x 21.0)

 

The Thermalright enables higher overclocks by removing heat quickly enough allowing us to increase the voltage to the CPU. While roughly 1.35V is the limit for the retail cooler, The Thermalright MUX-120 let us go up to 1.40V. In both cases you need to have a well ventilated case.


Um, yeah.

Now for the actual overclocking results. We overclocked in two ways: 1) with turbo mode enabled and ensuring stability at all turbo frequencies (both single and multiple cores active), and 2) with turbo mode disabled simply going for highest clock speed.

The results are in the table below:

CPU Stock Clock Speed Max Overclock (Turbo Enabled) Max Overclock (Turbo Disabled)
Intel Core i7 870 2.93GHz

Default: 3.39GHz (154 x 22.0)

3C/4C Active: 3.70GHz
2C Active: 4.00GHz
1C Active: 4.16GHz

4.20GHz (200 x 21.0)
Intel Core i7 860 2.80GHz

3.23GHz (154 x 21.0)

3C/4C Active: 3.54GHz
2C Active: 3.85GHz
1C Active: 4.00GHz

3.99GHz (210 x 19.0)
Intel Core i5 750 2.66GHz

3.2GHz (160 x 20.0)

3C/4C Active: 3.96GHz
2C Active: 4.00GHz
1C Active: 4.16GHz

3.92GHz (206.5 x 19)

 

For best performance with all four cores active, disabling turbo mode is the way to go. Otherwise you have to reduce the BCLK in order to make sure your system is still stable when the one-active-core turbo mode kicks in. For example, with our Core i7 870 with turbo disabled we hit 4.2GHz using a 200MHz BCLK. If we used the same BCLK but left turbo enabled, when only one core was active we'd hit 5.4GHz - clearly not realistic with only air cooling.

The benefit of leaving turbo enabled is that you get a more balanced system that's not always using more power than it needs to.


The Core i5 750


Our Core i7 860 sample wasn't that great of an overclocker


Breaking 4.2GHz with our Core i7 870

 

At roughly 4GHz overclocks for all of these CPUs, it's reasonable to say that they are good overclockers. But how about with no additional voltage and the retail heatsink?

CPU Stock Clock Speed Max Overclock, Turbo Disabled (No Additional Voltage)
Intel Core i7 870 2.93GHz

3.37GHz (22 x 153MHz)

 

The stock overclocks just plain suck on Lynnfield, you need added voltage to overclock the chip. With more voltage it works just like a Bloomfield or Phenom II, but at stock voltages Lynnfield just doesn't clock very high. And it has nothing to do with yields.

Power Consumption Overclocking Lynnfield at Stock Voltage: We're PCIe Limited
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  • nikrusty - Wednesday, November 18, 2009 - link

    With this article Anandtech is Harder, Better, Faster Stronger.
    Seriously AWESOME ARTICLE! It cleared many of my doubts FLAT OUT! Now I know i5 is the way to go especially becoz I dont care about overclocking and just want good gaming performance...nothing screamingly extreme. Budget + Performance always keeps you level headed.
    Reply
  • shiro - Wednesday, October 21, 2009 - link

    what is that monster hoop of death heatsink that's on page 3? lol Reply
  • Eeqmcsq - Saturday, September 19, 2009 - link

    I asked a similar question in one of the other articles, so pardon me if this sounds repetitive.

    According to the Turbo charts, the slowest Turbo speed is higher than the stock speed. Why is that? For example, why not just make the 750 a stock GHz of 2.8 GHz instead of 2.66GHz?
    Reply
  • Eeqmcsq - Saturday, September 19, 2009 - link

    Argh, please ignore. Replied using the wrong Firefox tab. Reply
  • The0ne - Tuesday, September 15, 2009 - link

    Clear up what you're trying to show on the graphs please. You're getting more FPS at max setting than at min settings? Label the graphs like you did with the others please. With the others I can just look and understand what you're doing. With these, I'm scratching my head. Reply
  • The0ne - Tuesday, September 15, 2009 - link

    Ah, turbo mode represented in FPS >.>' Reply
  • kkara4 - Monday, September 14, 2009 - link

    over at bittech.net, they are saying that it is more worth it to go for the i7-920, if we are considering anything above the i5. this is a conflicting story, since anand is recommending the lynnfields. anand or anybody else for that matter could you please see their articles and tell me what they have done wrong? (or perhaps you guys failed to see something). Your article explains things in great technical detail which i can understand since i have studied microprocessors, hence i am more inclined to go for lynnfield. anyway if someone could cross check that would be good Reply
  • mapesdhs - Tuesday, September 15, 2009 - link


    If I've understood Anand's analysis correctly, the conclusion is that,
    for application mixes which involve a lot of single and/or dual-threaded
    codes, and assuming one is not interested in high-end SLI/CF setups
    or hard oc'ing all 4 cores all the time for tasks like video encoding
    or animation rendering, the 750/860 are better buys because they
    will internally push 1-core and 2-core clocks to a higher rate than
    occurs with the 920 via the Turbo function, giving better results
    than the 920, and of course the 750/860 are cheaper solutions
    (although the 860 price is similar to the 920, the mbd costs less
    than an X58, from what people say).

    So it depends on what you want to use your system for. No interest
    in CF/SLI? Running games that don't hammer 4 cores? An i5 750 or
    i7 860 makes more sense. Using apps that don't use more than 2 cores?
    Again the 750/860 is more logical, especially from a cost viewpoint.

    This ties in with the other advantage of the X58 platform, ie. the
    upgrade path to 6-core and 8-core CPUs. If this is something that
    holds no value to you, then P55 makes more sense.

    As always, it depends on what you want to use the system for. The
    attraction of the 860 from a more general point of view is that it
    also offers good quad-core performance when one does use all 4 cores
    without sacrificing the traditional higher-clocks possible with
    single or dual core setups when one is only using 1 or 2 cores. It's
    the best of both worlds, at least for out-of-the-box functionality
    anyway.

    However, if one does intend to use all 4 cores almost all the time
    (I do) with a strong overclock, then the 920 is a better choice
    because of the voltage issue and (IMO) the 6/8-core upgrade path.
    Likewise, high-end multi-GPU setups work better with X58.

    Given that general usage of a PC rarely uses more than 2 cores, this
    is why the 750 and 860 are such attractive options.

    As for the 870, despite its 1/2-core speed advantages, the price is
    too high IMO. For that kind of money, a 920 makes more sense, paired
    with better cooling if one has such a spare budget, or buy a better
    GPU setup which, for gaming, is where the real bottleneck lies.

    Anand, please correct me if I'm wrong with the above.

    Ian.

    PS. As always, real-world pricing issues can make a mess of on-paper
    technical conclusions. Also, although many games/apps don't exploit
    more than 2 cores now, this is likely to change in the near future as
    multi-core coding becomes more pervasive in the industry.

    Reply
  • mapesdhs - Monday, September 14, 2009 - link


    Anand/Gary,

    Re your comments about an X58 advantage being the ability to use
    later 6 and 8-core CPUs...

    I've been planning to build an i7 920 system for video encoding, so
    a max oc on all cores is useful to me; from the article I thus infer
    the X58 is a better choice.

    However, if I did buy such a setup instead of an i5 or i7 860, what
    would the cost tradeoff be do you think when the 6-core CPUs arrive
    with respect to upgrading? By that I mean, for total processing
    throughput, do you reckon a 6-core upgrade would be significantly
    cheaper than simply buying a second i7 920 setup? (gfx not an issue)
    If not, then the ability to use 6/8-core CPUs later in this context
    is somewhat lessened, something that would apply to animation
    rendering aswell (ie. extra complete systems perhaps more cost
    effective in increased overall throughput compared to upgrading to
    more cores). Any ideas? Also, unless the applications used can
    exploit more than 4 cores, the later 6-core CPUs won't help. I have
    about 1500 hours of material to convert to DivX. Each file is about
    40 to 45 minutes (documentary), so converting multiple files on
    multiple systems at the same time is very doable.

    Given the above, I'm looking forward to more details on how a max
    oc'd i860/i870 compares to a max oc'd 920.

    At present I'm just using a 6000+ setup to work out the appropriate
    format/conversion paths.

    Ian.

    PS. May I suggest you don't bother replying to those moaning in such
    an obviously ludicrous manner about the Turbo mode being active? I
    have the distinct impression their posts are designed purely to
    irritate. Please don't encourage them. Anyone with any sense will
    read the article and understand the salient points you've highlighted
    about Turbo mode being an integral function of the chip.

    Reply
  • Milleman - Sunday, September 13, 2009 - link

    I would say that i5 750 and Pehnom II X4 965 is fully comparable. AMD just have to adjust the pricetag and the price/performance will be on par. Looking at the Gaming rig performance, both i5 750 and Pehnom II X4 965 are well enough for gaming pleasure. I wouldn't shell out my bucks for the more expensive Intel top models. It's such a waste of money, unless you are working with huge video and image editing processes. Reply

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