Intel gave us a really neat tool when they launched Core i7 called Turbo Boost. This dynamically adjusts the CPU speed based on the workload it has and some other factors like voltage and temperature. It's a really neat idea that kind of automatically overclocks the CPU, without all of the hassle of testing for stability. The idea is that when you need all four of your cores, you'll get a moderate single-bin boost, but when your only using one or two of them, the gain is bigger.

With the initial run of Core i7s on the LGA 1366 socket, Turbo Boost was fairly insignificant, only giving a maximum 266mhz overclock by default. This is accomplished by raising the CPU's multiplier by 2 "bins." When all four cores are loaded, an Intel Core i7 900 series CPU will only raise the multiplier by a single bin, or 133mhz. When Intel launched Lynnfield, or the Core i7/i5 for Socket 1156, we got a peak at what Turbo Boost's potential could really be.

On my Core i7 860, Turbo Boost will raise the CPU speed from 2.8ghz all the way up to 3.46ghz, or a maximum of 5 speed bins. That makes it quite competitive in single-threaded workloads with the much more expensive Core i7 960, however in multi-threaded workloads that advantage diminishes. When two or more cores are loaded, your gain is more likely to be only 2 bins, but still more than the single bin you get with a Core i7 900-series CPU, and that gain keeps the 800-series running with the big dogs.

The real fun is when we couple Turbo Boost with overclocking (insert evil laugh here). For the test, I took an Asus P7P55D motherboard, just like the one in Njord 1156, and a Core i7 860. I installed some Corsair XMS DDR3-1600 and activated the XMP profile for it in the BIOS, giving me the best timings that Corsair can muster. I then raised the CPU voltage to 1.3v and cranked the BCLK frequency to 166mhz. This means that each bin increase that Turbo Boost gives us now is a 166mhz overclock, instead of 133mhz. Check out the results:

Full Load                 Single Load

That's right, a staggering 4.16ghz when only a single core is active, and a 3.66ghz clock speed when all cores are loaded. When I attempted to get this chip to 4ghz the traditional way, I ended up having to throw so much voltage at it that it overheated. Being able to relax the BCLK and just let Turbo Boost do it's thing, I've achieved over 4ghz operation when the chip can handle it, and quite good 3.6ghz operation when it's really crunching. This means while gaming, I've actually got a higher clock speed than I could have had otherwise, and I have a very cool and stable machine.

With better cooling, I might push this a little harder, but for now I'm very content with this very doable overclock. Thanks Intel!