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.
Facebook
Twitter
RSS
283 Comments
View All Comments
-=Hulk=- - Monday, January 3, 2011 - link
That's crazy, are the chipsets PCI-e line still limited to v1 (250MB/s) speed or what????http://images.anandtech.com/reviews/cpu/intel/sand...
mino - Monday, January 3, 2011 - link
No, you read it wrong.There are altogether 8 PCIE 2.0 linex and all can be used independently, aka s as "PCIe x1".
The CPU-Chipset bandwith however is a basic PCIe x4 link, so do not expect wonders is more divices are in heavy use ...
-=Hulk=- - Monday, January 3, 2011 - link
No!Look at the PCI-e x16 from the CPU. Intel indicates a bandwidth of 16GB/s per line. That means 1GB/s per line.
But PCI-e v2 has a bandwidth of 500MB/s per line only. Thats mean that the values that Intel Indicates for the PCI-e lines are the sum of the upload AND download bandwidth of the PCI-e.
Thats means that the PCI-e lines of the chipset run at 250MB/s speed! That is the bandwidth of the PCI-e v1, and Intel has done the same bullshit with the P55/H57, he indicates that they are PCI-e v2 but they limits their speed to the values of the PCI-e v1:
P55 chipset (look at the 2.5GT/s !!!) :
"PCI Express* 2.0 interface:
Offers up to 2.5GT/s for fast access to peripheral devices and networking with up to 8 PCI Express* 2.0 x1 ports, configurable as x2 and x4 depending on motherboard designs.
http://www.intel.com/products/desktop/chipsets/p55... "
P55, also 500MB/s per line as for the P67
http://benchmarkreviews.com/images/reviews/motherb...
Even for the ancient ICH7 Intel indicates 500MB/s per line, but at that time PCI-e v didn't even exist... That's because it's le sum of the upload and download speed of the PCI-e v1.
http://img.tomshardware.com/us/2007/01/03/the_sout...
DanNeely - Monday, January 3, 2011 - link
Because 2.0 speed for the southbridge lanes has been reported repeatedly (along with a 2x speed DMI bus to connect them), my guess is an error when making the slides with bidirectional BW listed on the CPU and unidirectional BW on the southbridge.jmunjr - Monday, January 3, 2011 - link
Intel's sell out to big media and putting DRM in Sandy Bridge means I won't be getting one of these puppies. I don't care how fast it is...Exodite - Monday, January 3, 2011 - link
Uh, what exactly are you referencing?If it's TXT it's worth noting that the interesting chips, the 2500K and 2600K, doesn't even support it.
chirpy chirpy - Tuesday, January 11, 2011 - link
I think the OP is referring to Intel Insider, the not-so-secret DRM built into the sandy bridge chips. I can't believe people are overlooking the fact that Intel is attempting to introduce DRM at the CPU level and all everyone has to say is "wow, I can't WAIT to get one of dem shiny new uber fast Sandy Bridges!"I for one applaud and welcome our benevolent DRM overlords.....
http://www.pcmag.com/article2/0,2817,2375215,00.as...
nuudles - Monday, January 3, 2011 - link
I have a q9400, if I compare it to the 2500K in bench and average (straight average) all scores the 2500K is 50% faster. The 2500K has a 24% faster base clock, so all the architecture improvements plus faster RAM, more cache and turbo mode gained only ~20% or so on average, which is decent but not awesome taking into account the c2q is 3+ year old design (or is it 4 years?). I know that the idle power is significantly lower due to power gating so due to hurry up and wait it consumes less power (cant remember c2q 45nm load power, but it was not much higher than this core 2011 chips).So 50%+ faster sounds good (both chips occupy the same price bracket), but after equating clock speeds (yes it would increase load and idle power on the c2q) the improvement is not massive but still noticeable.
I will be holding out for Bulldozer (possibly slightly slower, especially in lightly threaded workloads?) or Ivy Bridge as mine is still fast enough to do what I want, rather spend the money on adding a SSD or better graphics card.
7Enigma - Monday, January 3, 2011 - link
I think the issue with the latest launch is the complete and utter lack of competition for what you are asking. Anand's showed that the OC'ing headroom for these chips are fantastic.....and due to the thermals even possible (though not recommended by me personally) on the stock low-profile heatsink.That tells you that they could have significantly increased the performance of this entire line of chips but why should they when there is no competition in sight for the near future (let's ALL hope AMD really produces a winner in the next release) or we're going to be dealing with a plodding approach with INTEL for a while. In a couple months when the gap shrinks (again hopefully by a lot) they simply release a "new" batch with slightly higher turbo frequencies (no need to up the base clocks as this would only hurt power consumption with little/no upside), and bam they get essentially a "free" release.
It stinks as a consumer, but honestly probably hurts us enthusiasts the least since most of us are going to OC these anyways if purchasing the unlocked chips.
I'm still on a C2D @ 3.85GHz but I'm mainly a gamer. In a year or so I'll probably jump on the respin of SDB with even better thermals/OC potential.
DanNeely - Monday, January 3, 2011 - link
CPUs need to be stable in Joe Sixpack's unairconditioned trailer in Alabama during August after the heatsink is crusted in cigarette tar and dust, in one of the horrible computer desks that stuff the tower into a cupboard with just enough open space in the back for wires to get out; not just in an 70F room where all the dust is blown out regularly and the computer has good airflow. Unless something other than temperature is the limiting factor on OC headroom that means that large amounts of OCing can be done easily by those of us who take care of their systems.Since Joe also wants to get 8 or 10 years out of his computer before replacing it the voltages need to be kept low enough that electromigration doesn't kill the chip after 3 or 4. Again that's something that most of us don't need to worry about much.