Corsair blog

Since late 2003 and the announcement of the Intel® Pentium® 4 EE, having an unlocked processor multiplier used to mean shelling out almost $1,000 USD. While Intel previously launched an Intel Pentium Dual-Core E6500K processor that was unlocked it was not widely available. However, the new Intel Core™ i5 655K and Intel Core i7 875K processors, will be widely available as part of the “K” series of unlocked processor. Two benefits of having an unlocked multiplier include the fine tuning frequencies and higher overclock potential, which can really be seen when using extreme cooling.

Let’s take a look at the specs of the two processors, both of which work in existing socket 1156 motherboards. First, we have the Core i5 655K, a 3.2GHz 32nm dual core processor with Intel Hyper-Threading Technology. This processor has a stock multiplier of 24x with a base clock of 133MHz. It also includes an integrated 45nm graphics processor similar to the other processors in the Clarkdale family. The second unlocked processor is the Intel Core i7 875K, a 2.93GHz 45nm quad core processor with Intel HT Technology. The stock multiplier on this processor is 22x with a base clock of 133MHz. This processor is part of the Lynnfield family which includes the Intel Core i7 860 and 870.

Overclocking these processors is very similar to that of any of the previous Intel Core i3, Core i5, and Core i7 socket 1156 processors. However, a new feature is that you are able to dial in the optimal base clock and memory clocks while adjusting the CPU frequency with the multiplier. In addition, the multiplier unlock will also help your overclock if you run into a base clock wall due to the motherboard or other limitations.

System Configuration

• Intel Core i5 655K/Core i7 875K
• 4GB of Corsair Dominator® GT DDR3 memory (CMGTX2)
• EVGA P55 Classified
• NVIDIA GeForce GTX 480
• Corsair Professional Series 850HX power supply
• Corsair Performance Series P64 SSD
• Corsair Hydro Series H50 CPU Cooler

The Intel Core i5 655K overclocked just as well as the previous Clarkdale processors reaching 4.5GHz, a full 1.3GHz overclock from stock. With the unlocked processor I was able to raise the multiplier to 25x with a base clock of 180MHz which seemed to be the best for this configuration. The overclock yielded 30-40% increases in 2D and 3D benchmarks, except for 3Dmark Vantage where there was only a 3% increase. This was due to the fact that the score is heavily GPU weighted.

The Core i7 875K overclocked to 4.05GHz again over 1GHz overclock on the processor. The performance gains again were anywhere from 32%-38% while 3DMark Vantage saw the same 3.74% increase. The additional two cores on the 875K did give a nice boost as well in the multi-threaded benchmarks. However the 655K was able to achieve a better overclock which allowed it to do better in the single threaded benchmarks.

In order to take full advantage of these processors you will want to ensure your motherboard supports these processors, in addition to updating the bios with support for these processors. You will also need to enable Turbo mode within the motherboards bios in order to adjust the multiplier above the stock 22x or 24x. If Turbo mode is not enabled the bios may let you set the desired multiplier however the processor will not run at that multiplier.

The new unlocked Intel Core i7 and Core i5 processors are priced well considering an Intel Core i7 Extreme Edition unlocked processor is around $1000. If you are running into a base clock or other limitation the unlocked multiplier may help achieve a higher processor frequency. I would expect to see the 655K pushing frequencies near 7GHz by some of the extreme overclockers.