The Sandy Bridge Review: Intel Core i7-2600K, i5-2500K and Core i3-2100 Tested
by Anand Lal Shimpi on January 3, 2011 12:01 AM ESTOverclocking, the K-Series and What You’ll Want to Buy
If you haven’t noticed, the computing world is becoming more integrated. We review highly integrated SoCs in our smartphone coverage, and even on the desktop we’re seeing movement towards beefy SoCs. AMD pioneered the integrated memory controller on desktop PCs, Intel followed suit and with Lynnfield brought a PCIe controller on-die as well. Sandy Bridge takes the next logical step and brings a GPU on-die, a move matched by AMD with Brazos and Llano this year.
In the spirit of integration, Intel made one more change this round: the 6-series chipsets integrate the clock generator. What once was a component on the motherboard, the PLL is now on the 6-series chipset die. The integrated PLL feeds a source clock to everything from the SATA and PCIe controllers to the SNB CPU itself. With many components driven off of this one clock, Intel has locked it down pretty tight.
With Nehalem and Westmere, to overclock you simply adjusted the BCLK from 133MHz to whatever speed you wanted and sometimes toyed with multipliers to arrive at a happy end result. With Sandy Bridge, the BCLK generated on the 6-series PCH is at 100MHz by default and honestly won’t go much higher than that.
While I’ve heard reports of getting as high as 115MHz, I’d view 103—105MHz as the upper limit for what you’re going to get out of BCLK overclocking. In other words: next to nothing. A 105MHz BCLK overclock on a Core i7-2600 will take you from a stock speed of 3.4GHz to a whopping 3.57GHz. The form of overclocking we’ve been using for the past decade is effectively dead on Sandy Bridge.
Years ago, before the Pentium II, we didn’t rely on BCLK (or back then it was just FSB or bus overclocking) to overclock. Back then, if we wanted a faster CPU we’d just increase the clock multiplier. Intel has dabbled in offering multiplier unlocked parts for overclockers, we saw this last year with the Core i7 875K for example. With Sandy Bridge, those unlocked parts are going to be a lot more important to overclockers.
It works like this. If you have a part that does not support Turbo (e.g. Core i3-2100 series), then your CPU is completely clock locked. You can’t overclock it at all, have fun at your stock frequency. This is good news for AMD as it makes AMD even more attractive at those price points.
If you have a part that does support turbo (e.g. Core i5-2400), then you have what’s called a “limited unlocked” core—in other words you can overclock a little bit. These parts are limited to an overclock of 4 processor bins above and beyond the highest turbo frequency. Confused yet? This chart may help:
In this case we’re looking at a Core i5-2500, which runs at 3.3GHz by default. When a single core is active, the chip can turbo up to 3.7GHz. If you want, you can change that turbo state to go as high as 4.1GHz (if your CPU and cooling can keep up).
Overclocking these limited unlocked chips relies entirely on turbo however. In the case above, the fastest your chip will run is 4.1GHz but with only one core active. If you have four cores active the fastest your chip can run is 3.8GHz. While Intel didn’t sample any limited unlocked parts, from what I’ve heard you shouldn’t have any problems hitting these multiplier limits.
There’s a third class of part: a fully unlocked K-series chip. At launch there are only two of these processors: the Core i5-2500K and the Core i7-2600K. Anything with a K at the end of it means you get all multipliers from 16x all the way up to 57x at your disposal. It’s effectively fully unlocked.
These chips overclock very well. Both my Core i5-2500K and Core i7-2600K hit ~4.4GHz, fully stable, using the stock low-profile cooler.
This is all you need for 4.4GHz
With a bit more effort and a better cooler, you can get anywhere in the 4.6-5.0GHz range:
It's a bit too early to tell how solid these near-5GHz overclocks will be, but I'm confident in the sub-4.5GHz overclocks we were able to sustain.
You do pay a price premium for these K-series SKUs. The 2500K will cost you another $11 over a stock 2500 and the 2600K costs an extra $23. In the case of the 2500K, that’s a small enough premium that it’s honestly worth it. You pay $11 extra for a chip that is very conservatively clocked and just begging for you to overclock it. Even the 2600K’s premium isn’t bad at all.
| Model Number | Standard SKU | K-Series SKU | Price Premium |
| Intel Core i7-2600 | $294 | $317 | +$23 |
| Intel Core i5-2500 | $205 | $216 | +$11 |
As an added bonus, both K-series SKUs get Intel’s HD Graphics 3000, while the non-K series SKUs are left with the lower HD Graphics 2000 GPU.
Compared to Lynnfield, you’re paying $11 more than a Core i5-760 and you’re getting around 10-45% more performance, even before you overclock. In a perfect world I’d want all chips to ship unlocked; in a less perfect world I’d want there to be no price premium for the K-series SKUs, but at the end of the day what Intel is asking for here isn’t absurd. On the bright side, it does vastly simplify Intel’s product stack when recommending to enthusiasts: just buy anything with a K at the end of it.
Since we’re relying on multiplier adjustment alone for overclocking, your motherboard and memory actually matter less for overclocking with Sandy Bridge than they did with P55. On both P67 and H67, memory ratios are fully unlocked so you can independently set memory speed and CPU speed. Even the GPU ratios are fully unlocked on all platforms and fully independent from everything else.
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mosu - Monday, January 3, 2011 - link
If I want to spend every year a big lot of money on something I'll sell on eBay at half price a few months later and if I'd like crappy quality images on my monitor, then I would buy Sandy Bridge... but sorry, I'm no no brainer for Intel.nitrousoxide - Monday, January 3, 2011 - link
It really impressed me as I do a lot of video transcoding and it's extremely slow on my triple-core Phenom II X3 720, even though I overclocked it to 4GHz. But there is one question: the acceleration needs EU in the GPU, and GPU is disabled in P67 chipset. Does it mean that if I paired my SNB with a P67 motherboard, I won't be able to use the transcoding accelerator?nitrousoxide - Monday, January 3, 2011 - link
Not talking about SNB-E this time, I know it will be the performance king again. But I wonder if Bulldozer can at least gain some performance advantage to SNB because it makes no sense that 8 cores running at stunning 4.0GHz won't overrun 4 cores below 3.5GHz, no matter what architectural differences there are between these two chips. SNB is only the new-generation mid-range parts, it will be out-performed by High-End Bulldozers. AMD will hold the low-end, just as it does now; as long as the Bulldozer regain some part that Phenoms lost in mainstream and performance market, things will be much better for it. Enthusiast market is not AMD's cup of tea, just as what it does in GPUs: let nVidia get the performance king and strike from lower performance niches.strikeback03 - Tuesday, January 4, 2011 - link
I don't think we'll know until AMD releases Bulldozer and Intel counters (if they do). Seems the SNB chips can run significantly faster than they do right now, so if necessary Intel could release new models (or a firmware update) that allows turbo modes up past 4GHz.smashr - Monday, January 3, 2011 - link
This review and others around the web refer to the CPUs as 'launching today', but I do not see them on NewEgg or other e-tailer sites.When can we expect these babies at retail?
JumpingJack - Monday, January 3, 2011 - link
They are already selling in Malaysia, but if you don't live in Malasia then your are SOL :) ... I see rumors around that the NDA was suppose to expire on the 5th with retail availability on the 9th... I was thinking about making the leap, but think I will hold off for more info on BD and Sk2011 SB.slickr - Monday, January 3, 2011 - link
Intel has essentially shoot itself in the foot this time. Between the letters restrictions, the new chipset and crazy chipset differentiations between a P and a H its crazy.Not to mention they lack USB 3.0, ability to have an overclock mobo with integrated graphics and the stupid turbo boost restrictions.
I'll go even more and say that the I3 core is pure crap and while its better than the old core I3 they are essentially leaving the biggest market the one up the $200 dollars wide open to AMD.
Those who purchase CPU's at $200 and higher have luck in the 2500 and 2600 variants, but for the majority of us who purchase cpu's bellow $200 its crap.
Essentially if you want gaming performance you buy I3 2100, but if you want overall better performance go for a phenom II.
Hopefully AMD comes up with some great CPU's bellow the $200 range that are going to be with 4 cores, unlimited turbo boost and not locked.
Arakageeta - Tuesday, January 4, 2011 - link
It seems that these benchmarks test the CPUs (cores) and GPU parts of SandyBridge separately. I'd like to know more about the effects of the CPU and GPU (usually data intensive) sharing the L3 cache.One advantage a system with a discrete GPU is that the GPU and CPUs can happily work simultaneously without largely affecting one another. This is no longer the case with SandyBridge.
A test I would like to see is a graphics intensive application running while another another application performs some multi-threaded ATLAS-tuned LAPACK computations. Do either the GPU or CPUs swamp the L3 cache? Are there any instances of starvation? What happens to the performance of each application? What happens to frame rates? What happens to execution times?
morpheusmc - Tuesday, January 4, 2011 - link
To me it seems that marketing is defining the processors now in Intel rather than engineering. This is always the case but I think now it is more evident than ever.Essentially if you want he features that the new architecture brings, you have to sell out for the higher end models.
My ideal processor would be a i5-2520M for the desktop: Reasonable clocks, good turbo speeds (could be higher for the desktop since the TDP is not that limited), HT, good graphics etc. The combination of 2 cores and HT provides a good balance between power consumption and perfromance for most users.
Its desktop equivalent price-wise is the 2500, wich has no HT and a much higher TDP because of the four cores. Alternatively, maybe the 2500S, 2400S or 2390T could be considered if they are too overpriced.
Intel has introduced too much differentiation in this generation, and in an Apple-like fashion, i.e. they force you to pay more for stuff you don't need, just for an extra feature (eg. VT support, good graphics etc) that practically costs nothing since the silicon is already there. Bottomline, if you want to have the full functionality of the silicon that you get, you have to pay for the higher end models.
Moreover, having features for specific functions (AES, transcoding etc) and good graphics makes more sense in lower-end models where CPU power is limited.
This is becoming like the software market, where you have to pay extra for licenses for specific functionalities.
I wouldn't be surprised if Intel starts selling "upgrade licenses" sometime in the future that will simply unlock features.
I strongly prefer AMD's approach where all the fatures are available to all models.
I am also a bit annoyed that there is very little discusison about this problem in the review. I agree that technologically Sandy Bridge is impressive, but the artificial limiting of functionality is anti-technological.
ac2 - Tuesday, January 4, 2011 - link
Agreed, but, apart from the K-series/ higher IGP/ motherboard mess up (which I think should be shortly cleared up), all the rest of it is just smart product marketing...It irritates readers of AnandTech, but for the most people who buy off-the-shelf it's all good, with integrators patching up any shortcomings in the core/ chipset.
The focus does seem to be mobile, low-power and video transcode, almost a recipe for macbook!!