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Clarkdale And Turbo Boost

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

Intel currently has four Core i5 desktop dual-core processors at 3.2, 3.33, and 3.46 GHz. They all support the Turbo Boost feature, which means that the peak clock speed may be higher if there is sufficient thermal headroom and a high processor load. The following table provides the full overview on all processors currently available that are based on the Nehalem architecture:

Intel's Nehalem / Westmere Lineup For Q1/2010          

Code Name
Max. Turbo
Cores /Threads
Core i7-975 Extreme
Bloomfield3.33 GHz3.6 GHzYes45nm4/8130W$999
Core i7-950Bloomfield3.06 GHz3.33 GHzYes45nm4/8130W$562
Core i7-920Bloomfield2.66 GHz2.93 GHzYes45nm4/8130W$284
Core i7-870Lynnfield2.93 GHz3.6 GHzYes45nm4/895W$562
Core i7-860Lynnfield2.8 GHz3.46 GHzYes45nm4/895W$284
Core i5-750Lynnfield2.66 GHz3.2 GHzNo45nm4/495W$196
Core i5-670Clarkdale3.46 GHz3.73 GHzYes32/45nm2/473W$284
Core i5-661Clarkdale3.33 GHz3.6 GHzYes32/45nm2/487W$196
Core i5-660Clarkdale3.33 GHz3.6 GHzYes32/45nm2/473W$196
Core i5-650Clarkdale3.2 GHz3.46 GHzYes32/45nm2/473W$176
Core i3-540Clarkdale3.06 GHzN/AYes32/45nm2/473W$133
Core i3-530Clarkdale2.93 GHzN/AYes32/45nm2/473W$133
Pentium G6950
Clarkdale2.8 GHzN/ANo32/45nm2/273W$ 87

The 661’s graphics unit runs at 900 MHz while all other current i3/i5 models run at 733 MHz. We believe that the additional GPU speed is not a must-have feature, since few people would actually purchase a system with integrated graphics to run 3D-intensive applications or games. If you ask us, you should either choose one of the 73W models for multimedia systems or buy a discrete graphics card if you're planning on serious gaming. Although Intel has made quite a step forward here, integrated graphics still won’t impress anyone with enthusiast cred.

The main difference between Core i3 and i5 is the absence of Turbo Boost on Core i3. In addition, the Core i5 desktop processors all support Intel’s AES New Instructions (AES-NI) to accelerate encryption or decryption; Core i3 doesn’t, nor do its clock speeds reach as high. Still, due to Core i3's low price points and the fact that low-end chip overclocking margins that are typically only slightly behind the faster models, these should provide great bang for the buck.

Turbo Boost in Action

Turbo Boost can accelerate the Core i5-661's processor clock by one 133 MHz clock speed increment for both cores, or by two speed bins for a single core.

The idle clock speed of 1,200 MHz is set by the SpeedStep feature, which kicks in when there is little or no work for the processor to do.

The nominal clock speed of 3.33 GHz is either reached during normal operation with constant processor load or if thermal conditions prevent Turbo Boost from accelerating the processor any further. In the screenshot above, Turbo Boost provides an additional 133 MHz (3.46 rather than 3.33 GHz) for both cores.

If we throw a single-threaded workload at the CPU it will accelerate by two 133 MHz speed increments, to 3.6 GHz.

Since Turbo Boost is a very handy, practical feature, we believe it makes sense to overclock the processor in a way that maximizes Turbo Boost speed, but leaves the nominal speed considerably lower for the sake of power consumption. Traditional overclocking sets the CPU to a fixed clock speed, which may be fast, but is also inefficient.

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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