Intel Core i7 920 940 965 Review & Overclocking - PAGE 29

Overclocking

Overclocking the Core i7 processors was an interesting experience, one very reminiscent of overclocking AMD's Phenom's.

Intel's QPI "Quick Path Interconnect" is extremely similar to AMD's HT "HyperTransport", and since both the Phenom and the i7's also have on-board memory controllers, it should not be surprising that overclocking the parts is very similar in some ways.

Core i7 965 Extreme Overclocking

This is the new high-end "Extreme" series processor from Intel, and boy does it show it (in performance).

The Core i7 965 derives its nominal 3.2GHz clock rate by multiplying its 133MHz base clock by 24 - which is 3.2GHz.

Intel however introduced its "Turbo" mode, which automatically increases the multiplier to 25 when more than one core is loaded, or to 26 when only one core is loaded - so the nominally 3.2GHz processor runs at 3.33GHz under load, and up to 3.46GHz when only one core is loaded - without any overclocking on the users part.

There are two ways of overclocking the Core i7 965 - increasing the base clock rate, which also increases the memory speed and the QPI speed, or just increasing the "Turbo" mode multipliers. Modest overclocks can be achieved without raising the core voltage, but as I wanted to find out the air cooled limits of the i7 965, I went up all the way to the maximum 1.65V that Intel tells everyone NOT to pass.

The i7 965 we have had a 130W TDP, and a default Vcore of 1.15V - so I bumped it to 1.4V with a 250mV dynamic voltage override.

I was then able to enjoy the Core i7 965 running at a quite decent 4.05GHz - totally stable.

I was able to go higher, but it was unstable, and I did not want to exceed 1.65V as I did not want to take a chance on burning out our only 965.

I also wanted to see how far I could push the QPI, so I backed down to a multiplier of 24, and increased the bus speed until the system was unstable, then backed down. The system was stable up to an FSB of 150MHz, for a 7.2GHz QPI rate with the DDR3 memory running at 1200MHz with 7-7-7-20-2T timing. Pretty impressive.

Core i7 940 Overclocking

Based on what I learned from the i7 965 overclocking, I suspect that an i7 940 would overclock to at least 3.3GHz, perhaps far more - see my i7 920 results :-)

Core i7 920 Overclocking

Unfortunately the Core i7 920 has a maximum 20x "normal" and 21x "Turbo" multiplier, which cannot be adjusted in the motherboards BIOS, so I knew I'd be QPI and memory speed limited.

From my i7 965 testing, I knew that I could reach at least 7.2GHz QPI data rate, and at least 1200MHz DDR3 rate - however given the low multiplier, I had to try to go as far beyond a 133MHz base clock rate as I could.

Learning as I went, I had to adjust the QPI rate down to "official" 4.8GHz, and the memory timing to 8-8-8-24 - but after a lot of re-boots, and complaints from my co-workers about the "beep-beep-beep" the motherboard made on failed overclocks, I finally was able to reach the highest base clock I could get stable - 174MHz, a 30.8% increase over the stock 133MHz.

One problem I had was with the memory multiplier - even though the BIOS claims to support a 6x memory multiplier, it did not work for me, so I had to stay with an 8x memory multiplier; which in turn, based on the 1.65V maximum memory voltage, limited how far I could push the base clock. Frankly, with the 6x multiplier working, I would not be surprised if I could have reached a 200MHz base clock!

I can't wait to get my hands on some nice third party overclocking boards, I think 4GHz ought to be quite reachable with an i7 920.