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A screenshot after applying on my machine:I'd been puzzling for a while why my Core i7 920 never reached the maximum Turbo Mode multiplier of 22, and finally managed to figure it out. So I thought I'd share...
The Turbo Mode is enabled when the OS is requesting full speed and the processor decides it's operating within current, temperature and power limits. It can then push the multiplier up to a maximum value, as long as it stays within those limits.
Each processor has 4 maximum values, depending on whether 1,2,3 or 4 cores are "active". The idea is that the fewer cores you have active, the faster they can go.
For the 920, 940 and 965, the maximum multiplier with 2 or more active cores is 1 above the standard - an extra 133MHz at standard BCLK. The maximum multiplier with only 1 active core is set to 2 above the standard - an extra 266MHz. And in the 965, you can change these settings; they're fixed in the 920 and 940.
Now, the important detail is what is meant by "active cores". For the purpose of Turbo Mode a core is "active" if it is in C0 (run) or C1/C1E (halt) state. A core is "inactive" if it is in C3 or C6 low-power state.
So for Turbo Mode to function effectively, in the BIOS you must have Intel(R) C-STATE Tech = Enabled. Otherwise the cores will never go lower than C1/C1E, and all four cores will always be "active" from the point of view of the Turbo Mode, so you'll never get the higher multiplier. C-STATE Tech is Disabled by default in the P6T BIOS.
With C-STATE Tech off, running 1 thread of Prime95, my 920 stays continuously at x21. Turning C-STATE Tech on, it fluctuates between x21 and x22, depending on how much other stuff is going on on the machine. It doesn't seem to make much difference whether Prime95 is tied to 1 core (via the Task Manager affinity setting), or hops between cores as is the default - either way, there's frequently only 1 core active at a time, so the x22 multiplier can kick in.
- TurboMode.jpg (77.05 KiB) Viewed 7189 times
