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Clarkdale Efficiency: The Perfect Clock Rate For Intel's Core i5-661

Clarkdale Efficiency: The Perfect Clock Rate For Intel's Core i5-661

Almost every processor can be easily overclocked on a decent motherboard. However, at some point, you'll have to boost the voltage to reach faster clock speeds, causing the processor to consume a lot more power.

There is a point at which every processor delivers its best performance per watt, though, and it happens way before you hit the chip's maximum overclock. Now it's time to determine this perfect clock speed for Intel's new Clarkdale dual-core architecture, which we know as the Intel Core i3 and Core i5.

We already executed this type of analysis on several other systems and discovered some interesting facts:

  • In the case of a Phenom II X4 quad-core (Deneb) on the Socket AM3 interface, the best performance at acceptable power consumption is reached at roughly 3.6 GHz.

Read the article Optimizing Your Phenom II Overclock For Efficiency

  • For a Core 2 Duo E8000-series (Wolfdale), based on the LGA 775 interface, the most efficient overclock speed is about 3.8 GHz.

Read the article Overclocking Core 2 Duo: Power Versus Performance

  • The Core i7-900-series quad-core (Bloomfield) running on an LGA 1366  interface delivers best performance per watt at 3.66 GHz.

Read the article Overclocking Core i7: Power Versus Performance

  • Finally, we also analyzed efficiency on the Core i5-700-series quad-core (Lynnfield) for LGA 1156 and found efficiency to be best at 3.2 GHz, with the Turbo Boost feature enabled and pushing performance up to 3.84 GHz.

Read the article Efficiency Explored: What’s The Perfect Clock Rate For Your Core i5?

While the 45nm Core 2 Duo reached top performance per watt at about 3.8 GHz, we expected higher clock speeds on the Core i5 dual-cores. Although the graphics unit is integrated with the processor, the new chips have a substantial advantage, thanks to Intel's new 32nm process.

Many online sites have reported getting Core i5 dual-cores to 4.2 or even 4.5 GHz on air cooling with comparatively little effort. You'll even find reports of hitting 6 to 7 GHz using liquid nitrogen, which is proof of the architecture having lots of overclocking headroom. Perhaps we'll even be able to reach 5 GHz on air cooling once Intel releases modified processor steppings in the next few months.

We grabbed our Core i5-661 dual-core sample (3.33 GHz nominal clock speed, 3.60 GHz with Turbo Boost operating on a single core, 900 MHz graphics clock speed) and overclocked it by raising the base clock (BCLK). At this point, it's important to watch the graphics core’s clock speed, as it also derives from the system’s base clock. Our overclocking focused on increasing the base clock in an effort to boost the processor’s nominal speed, leaving Turbo Boost and all power saving features, such as C-steps and SpeedStep, enabled.

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  • 0 Hide
    JohnnyLucky , February 17, 2010 5:12 AM
    Thanks for an informative overclocking article that helps put things in perspective.
  • 0 Hide
    shubham1401 , February 17, 2010 6:15 AM
    Nice article!!

    These i5 are good overclock-able chips :) 
  • 0 Hide
    racermx187 , February 17, 2010 6:30 AM
    Very nice article and I totally agree with the conclusion paragraph and changing the way CPUs are looked at for use.
  • 0 Hide
    anamaniac , February 17, 2010 7:43 AM

    But after all that, I'm just wondering what kind of efficiency I could get out of a high binned dual core that's left on stock clocks but heavily undervolted with 2x2GB 1.5v DDR3, a 80GB x18-m and a 5670 and a board/PSU designed for low powert usage. Hell, my current CPU would use as much power as that entire system. =)
    But, we didn't buy i7's for the performance-to-watt ratio now, did we?
  • 0 Hide
    JeanLuc , February 17, 2010 8:06 AM
    Patrick Schmid and Achim Roos - Can I ask why are your articles are always co-authored?

    Thank you.
  • 1 Hide
    coldmast , February 17, 2010 1:51 PM
    JeanLucPatrick Schmid and Achim Roos - Can I ask why are your articles are always co-authored? Thank you.

    The co-authoring probably has to do with one being the writer of the original article and the other being the translator, or one is the SME and the other is the technical writer.
  • 0 Hide
    envolva , February 17, 2010 3:07 PM
    We could use a i5 750 at stock speed to see how it compare with an overclocked i5 661. Maybe throw an i3 in there too to keep things in perspective.

    It would be nice to see Turbo Boost disabled (power savings still up) and see how the overal efficiency behaves. Whitout Turbo Boost, you can keep the multiplier under control maybe reducing the core voltage needed.
  • 0 Hide
    burnley14 , February 17, 2010 4:24 PM
    Pretty interesting that there was not much of an efficiency increase even with small overclocks. Maybe this is because of Turbo Boost? If so, I think envolva's got the right idea.
  • 0 Hide
    Anonymous , February 17, 2010 5:54 PM
    My question is what role the 45 nano graphics core plays in this?

    Might have been more interesting to use a i5-670 part, where the base core speed is 133 mhz higher and graphics core starts at 733 mhz versus 900.

    The power/clock speed graph looks a little odd, I wonder how much of it is the cpu core staying low power while the graphics core uses more and more energy?
  • -1 Hide
    ta152h , February 17, 2010 8:10 PM
    I'd be curious if overclocking the graphics part increases pure processor performance at all. The knee-jerk reaction is that this is an idiotic question, but consider the memory controller is in the video controller, and there's a possibility that even if you don't use the IGP, you might be well to overclock it to improve the memory performance slightly.
  • -1 Hide
    sandypants , February 17, 2010 8:41 PM
    What were the temperatures like?
  • -1 Hide
    Anonymous , February 18, 2010 9:27 AM
    I must say that in my mind your testing is faulty from the start: if you just start increasing base clock with stock voltages, the outcome is obvious even without testing (that best efficiency is around the point you can go without rising voltages). If you want to get us some real and even remotely useful data on microarchitecture/manufacturing process efficiency you must UNDERVOLT every test frequency you use down to minimum stable voltage! So any chance we will see that in future?
  • -2 Hide
    fernandogmd , February 18, 2010 2:38 PM
    It would´ve been interesting to see some game benchmarks as well. To see if there´s any benefit to efficiently overclock the cpu for games.
  • 0 Hide
    teknic111 , February 18, 2010 5:48 PM
    I want Gulftown!!!
  • 0 Hide
    Catalina588 , February 19, 2010 12:44 AM
    Is it just me, or did I miss the Voltage Table on the Voltage Table and Settings page? What voltages were used at each BCLK?
  • 0 Hide
    Anonymous , February 20, 2010 9:27 PM
    It's not just you.
  • 0 Hide
    tiktianc , February 22, 2010 2:59 AM
    i think there should be a effeciency article done for an i3, i mean they're really easy to overclock with the one in my mITX system doing 3.8GHz easy on stock cooler