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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Exodite - Monday, January 3, 2011 - link
I'm of two minds about that really.I had really set my mind on the 2500K as it offers unparalleled bang-for-buck and real-world testing have shown that Hyper-threading makes little difference in games.
With the compile tests it's clear there's a distinct benefit to going with the 2600K for me though, which means this'll end up more expensive than I had planned! :)
Lazlo Panaflex - Monday, January 3, 2011 - link
FYI, the 1100T is missing from several of the gaming benchmarks.....Melted Rabbit - Monday, January 3, 2011 - link
It wouldn't surprise me if that was intentional. I would hope that Anandtech reviewers were not letting companies dictate how their products were to be reviewed lest AT be denied future prerelease hardware. I can't tell from where I sit and there appears to be no denial that stating there is no such interference.In addition, real world benchmarks aside from games looks to be absent. Seriously, I don't use my computer for offline 3D rendering and I suspect that very few other readers do to any significant degree.
Also, isn't SYSMark 2007 a broken, misleading benchmark? It was compiled on Intel's compiler, you know the broken one that degrades performance on AMD and VIA processors unnecessarily. Also there is this bit that Intel has to include with its comparisons that use BAPco(Intel) benchmarks that include Intel's processors with comparisons to AMD or VIA processors:
Software and workloads used in performance tests may have been optimized for performance only on Intel microprocessors. Performance tests, such as SYSmark and MobileMark, are measured using specific computer systems, components, software, operations and functions. Any change to any of those factors may cause the results to vary. You should consult other information and performance tests to assist you in fully evaluating your contemplated purchase, including the performance of that product when combined with other products.
It isn't perfect, but that is what the FTC and Intel agreed to, and until new benchmarks are released by BAPco that do not inflict poor performance on non-Intel processors, the results are not reliable. I don't see any problem if the graph did not contain AMD processors, but that isn't what we have here. If you are curious, for better or for worse, BAPco is a non-profit organization controlled by Intel.
Anand Lal Shimpi - Monday, January 3, 2011 - link
Hardware vendors have no input into how we test, nor do they stipulate that we must test a certain way in order to receive future pre-release hardware. I should also add that should a vendor "cut us off" (it has happened in the past), we have many ways around getting supplied by them directly. In many cases, we'd actually be able to bring you content sooner as we wouldn't be held by NDAs but it just makes things messier overall.Either way, see my response above for why the 1100T is absent from some tests. It's the same reason that the Core i7 950 is absent from some tests, maintaining Bench and adding a bunch of new benchmarks meant that not every test is fully populated with every configuration.
As far as your request for more real world benchmarks, we include a lot of video encoding, file compression/decompression, 3D rendering and even now a compiler test. But I'm always looking for more, if there's a test out there you'd like included let me know! Users kept on asking for compiler benchmarks which is how the VS2008 test got in there, the same applies to other types of tests.
Take care,
Anand
Melted Rabbit - Tuesday, January 4, 2011 - link
Thanks for replying to my comment. I was understand why the review was missing some benchmarks for processors like the 1100T. I was also a bit hasty in my accusations with respect to interference from manufacturers, which I apologize for.I still have trouble with including benchmarks compiled on the Intel compiler without a warning or explanation of what they mean. It really isn't a benchmark with meaningful results if the 1100T is used x87 code and the Core i7-2600K used SSE2/SSE3 code. I would have no problem with reporting results for benchmarks compiled with Intel's defective compiler, like SYSmark 2007 and Cinebench R10 assuming they did not include results for AMD or VIA processors along with an explanation of why they were not applicable to AMD and VIA processors. However, not giving context to such results I find problematic.
DanNeely - Monday, January 3, 2011 - link
Sysmark2k7 is like the various 3dmark benches. Mostly useless but with a large enough fanbase that running it is less hassle than dealing with all the whining fanboi's/Anand Lal Shimpi - Monday, January 3, 2011 - link
There are a few holes in the data we produce for Bench, I hope to fill them after I get back from CES next week :) You'll notice there are some cases where there's some Intel hardware missing from benchmarks as well (e.g. Civ V).Take care,
Anand
Lazlo Panaflex - Monday, January 3, 2011 - link
Thanks Anand :-)MeSh1 - Monday, January 3, 2011 - link
Seems Intel did everything right for these to fit snuggly into next gen macs. Everthing nicely integrated into one chip and the encode/trascode speed boost is icing on the cake (If supported of course) being that Apple is content focused. Nice addition if youre a mac user.Doormat - Monday, January 3, 2011 - link
Except for the whole thing about not knowing if the GPU is going to support OpenCL. I've heard Intel is writing OpenCL drivers for possibly a GPU/CPU hybrid, or utilizing the new AVX instructions for CPU-only OpenCL.Other than that, the AT mobile SNB review included a last-gen Apple MBP 13" and the HD3000 graphics could keep up with the Nvidia 320M - it was equal to or ahead in low-detail settings and equal or slightly behind in medium detail settings. Considering Nvidia isn't going to rev the 320M again, Apple may as well switch over to the HD3000 now and then when Ivy Bridge hits next year, hopefully Intel can deliver a 50% perf gain in hardware alone from going to 18 EUs (and maybe their driver team can kick in some performance there too).