Under Core i7's Hood: Comparing The C0 And D0 Steppings

Core i7-965 (C0) Versus Core i7-975 (D0) At 3.33 GHz

Although the Core i7-965 Extreme is a 3.20 GHz processor, we decided to run 3.33 GHz in order to do a direct comparison to the Core i7-975 Extreme, which runs at 3.33 GHz by default. Since all Core i7 Extreme processors can easily be overclocked through a multiplier increase, and thanks to nice overclocking margins, this is definitely not a challenge for the processor.

Our first notable finding is the processor voltage, which differed quite a bit at this speed at peak loads:

The Core i7-965 Extreme, based on the C0 stepping, ran at 1.232 V effective voltage at the 3.33 GHz clock speed.

Meanwhile, it’s D0 counterpart, Core i7-975 Extreme, required a bit less: 1.136 V. This is a 8.45% difference and has a very measurable impact on system power consumption, which you’ll see in the benchmark section. Idle voltage was very similar, but there still are differences in system-wide power consumption.