When it comes to Intel processors, the word “unlocked” is not synonymous with low-priced mainstream products - it’s a feature normally reserved for flagship ‘Extreme Edition’ CPUs that bear higher price tags. Things are set to change today because Intel is launching the “unlocked” K series of processors to fit into the existing Lynnfield and Clarkdale line-up:

Processor Core (GHz)
Unlocked Turbo Frequency (GHz) Max Mem Clock Cores / Threads L3 Cache TDP
Intel Core i7-980X 3.33 Cores, DDR3, Power Up to 3.60 3 Channels
6 / 12 12MB 130W $999
Intel Core i7-870 2.93 DDR3, Power Up to 3.60 2 Channels
4 / 8 8MB 95W $562
Intel Core i7-875K 2.93 Cores, DDR3, Power Up to 3.60 2 Channels
4 / 8 8MB 95W $342
Intel Core i5-655K 3.20 Cores, DDR3, Power Up to 3.46 2 Channels
2 / 4 4MB 73W $216
Intel Core i5-650 3.20 DDR3 Up to 3.46 2 Channels
2 / 4 4MB 73W $176
Intel Core i3-540 3.06 DDR3 N/A 2 Channels
2 / 4 4MB 73W $133
Intel Core i3-530
2.93 DDR3 N/A 2 Channels
2 / 4 4MB 73W $113

While it is interesting that Intel is offering unlocked core multipliers on Lynnfield and Clarkdale, it’s more interesting that the models being introduced are not the most expensive in their respective families. Especially considering that the i7-875K’s stock speeds are identical to the i7-870 while costing less. At $349, it's only a stone's throw away from AMD's 1090T, while you've got the i7-860 coming in cheaper than both. All of these processors can be compared to one another in Bench here and here.

Overclockers will sit up and take note at the prospects of increased flexibility and the potential of alleviating bottlenecks caused by insufficient bus margins on cheaper processors. We've all had CPUs that seem to have additonal headroom for frequency scaling, but are held back because the highest available core multiplier ratio is too low.  We increase reference clock freqeuncies, only to find that some of the related busses aren't completely stable and as a result no choice but to fall back or relax key performance registers which defeats the purpose of performance related overclocking. That's one of the areas where the K-series might help. Another key factor that makes unlocked processors attractive is that they open the doors to easy overclocking for users that like to keep things simple. With unlocked multipliers we can overclock the CPU without having to fiddle around with memory ratios or memory timings, leaving those settings static.

As there are no under-hood changes to the substrates themselves, there’s not a whole lot of benchmarking for us to do in this review. We’ve already compared the performance of similarly clocked non K-series Lynnfield and Clarkdale processors in our platform launch articles and also have a range of comaprisons in Anandtech Bench. Our focus in this write-up is to look at how the i5-655K and i7-875K fit from an overclocking perspective against both their cheaper and more expensive counterparts.

Be for-warned that this isn’t a typical launch piece; it’s full of talk about voltages and harps on about overclocking in a way that will send many readers to sleep. If that isn’t a big enough deterrent, then read on…

Clarkdale 655K Overclocking
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  • Rajinder Gill - Saturday, May 29, 2010 - link


    I ran out of time to test any further unfortunately. The emphasis was kept on air/water cooling because it's practical to run 24/7.

  • TheBLK - Saturday, May 29, 2010 - link

    I'll ask again. Unless the screen shots are wrong you used BLK clock to over-clock rather than multiplier on the chip.

    Other reviews kept the BLK at the same value and just used the multiplier and seemed to get higher results.
  • Rajinder Gill - Saturday, May 29, 2010 - link

    Yes I did on the 655-K stock VID (added 2 BCLK because the next multiplier up was too far (133 multiples in frequency is a large jump) :

    Also describe why BCLK overclocking is not the way to go on the 655K for performance:


    Finally the 855K - this chip is limited to 4GHz even on water cooling. BCLK overclocking is not going to change that. 167 BCLK at DDR3 1670 is nowhere near stressful for the Lynnfield IMC. Multiplier overclocking is NOT going to make any difference to the clock speed limitation.

  • Rajinder Gill - Saturday, May 29, 2010 - link

    Just for you :)


    That is all the water loop can handle (the chip is drawing over 190W). I can drop the multiplier down to 30 (but then we are back to 4GHz).

    Hope this helps!

  • DJMiggy - Thursday, June 3, 2010 - link

    It seems like you guys used the wrong motherboard or got a dud i7. Other reviewers don't seem to be having as tough a time overclocking these higher.
  • Rajinder Gill - Friday, June 4, 2010 - link

    The motherboard is EVGA's E659 - works fine with my i7 870 ES taking it to 4.4GHz Linpack stable. It's the CPU that is the limiting factor here. Bear in mind that not all articles you've read will have stability checked stability with Linpack as well.

  • DJMiggy - Friday, June 4, 2010 - link

    That makes sense. Cool thanks! I appreciate the explanation.
  • ReaM - Saturday, June 5, 2010 - link

    I must say, what a crappy K-series! I can bring every i7 860 up to 4ghz. I have tested many of them, so there is really no reason to put any hope into these Ks. Just buy a regular one.

    My personal sample of 860 runs @ 4200 with 1.29V on air Noctua U12 with low temps.
  • ReaM - Saturday, June 5, 2010 - link

    Did you put Load Line Calibration into LVL2?
    I don't know what's that called on EVGA. Enhanced Power Slope. VDrop Adjustment. Lynnfield, unlike Bloomfield, likes their load line to be adjusted.
  • Rajinder Gill - Sunday, June 6, 2010 - link

    Makes no difference to the stability of this chip.

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