|Intel Core i7-2600K Sandy Bridge CPU|
|Reviews - Featured Reviews: Processors|
|Written by David Ramsey|
|Monday, 03 January 2011|
Page 13 of 15
Core i7-2600K Overclocking
The Cougar Point/Sandy Bridge platform brings major changes to the overclocking process. Here are the bullet points:
Overclocking by raising the motherboard's base clock is now all but impossible. Of the three P67-based motherboards I tried to overclock, the highest increase to the 100MHz base clock that I could get to run through stress testing was...103MHz. The Intel DP67BG motherboard wasn't stable above 102MHz, and couldn't run above 101MHz in stress testing. This limited overclocking ability is apparently because the P67's base clock is used to derive almost every other clock in the system, including the SATA and USB clocks. While having a single clock be the base for every other clock in the system probably means cheaper, more reliable motherboards, it removes an overclocking mechanism enthusiasts have used for many years.
Intel compensates for this by giving all Sandy Bridge processors unlocked multipliers: K-series processors get "fully unlocked" multipliers with no limits, while non-K series processors are "limited unlocked" CPUs that can only have their multipliers increased by a maximum of 4. All Sandy Bridge processors have fully unlocked video cores, RAM multipliers, and power settings, so you can tweak your RAM and on-board video with any motherboard, but for actual CPU core overclocking, you'll want a P67 Express motherboard.
Overclocking Sandy Bridge CPUs is different in another way, too. While everyone has their own overclocking techniques, I generally like to disable "turbo" features and run all processor cores as fast as I can under stress by raising the base multiplier. Well, you can't do this with the Intel Core i7-2600K: in fact, you can't increase the base multiplier at all! This was true in both the Intel DP67BG motherboard and ASUS motherboards I used, so I suspect this limitation is built into either the processor or the P67 chipset. Your only option is to increase the multiplier that will be used by Turbo Boost, and you can set individual multipliers to be used when 1, 2, 3, or all 4 cores are in use. Thus, if you disable Turbo Boost technology, you can't overclock the processor at all. Amusingly, Intel's press kit describes the the P67 Express/Sandy Bridge platform as having "flexible overclocking options"...
I had the best overclocking results from the ASUS P8P67 EVO motherboard. In the snazzy ASUS graphical EFI BIOS, you set the base clock and Turbo frequency in the "AI Tweaker" screen as shown below:
You can adjust the Turbo Boost settings for the Core i7-2600K in two ways: by all cores, or by individual cores. The first setting uses the same Turbo Boost ratio whether 1, 2, 3, or 4 cores are active; the second setting allows you to specify distinct multipliers for each situation. I'm interested in how much performance I can get when everything's active, so I used the "By All Cores" setting. This has the added advantage of being adjustable on the fly from inside Windows using ASUS' "Turbo V EVO" utility. However, you'd probably achieve overall better performance by hand-tweaking the multipliers used in each of the four possible Turbo Boost core configurations.
My best results came with a base clock of 103Mhz and an "all cores" ratio of 46, for a final clock speed of 4.738Ghz. This is better than it seems since the 3.8Ghz "maximum Turbo Boost" frequency Intel touts for the Core i7-2600K is when only one core is being stressed; the 4.738Ghz overclock achieved here is when all cores are being stressed. Under these circumstances the stock-clocked 2600K is only running at 3.5Ghz.
This overclock represents a solid 25% overclock from the standard 3.8Ghz Turbo Boost frequency, and applies to all four cores under load rather than the single core the stock 3.8Ghz applies to. This performance differential was reflected in the benchmarks. This is the highest "on air cooling" frequency I've seen with an Intel quad-core processor. I was initially disappointed that I wasn't able to break the 5Ghz barrier, but apparently only about 10% of the initial run of Core i7-2600K processors can do this.