Two highest speeds on Core 2 Duo

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Emme
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Two highest speeds on Core 2 Duo

Post by Emme » Sat 28. Nov 2009, 13:42

I noticed on many Intel Core 2 Duo CPUs that there are always two highest speeds, one is the highest speed "written on the box" (e.g. 2.40GHz), the other is a little bit higher (e.g. 2.41GHz) which usually has a much higher voltage.

What's the purpose of this?

Thanks

Martin

the-fallen
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Re: Two highest speeds on Core 2 Duo

Post by the-fallen » Sat 28. Nov 2009, 18:42

The one with the 100MHz higher frequency is the SpeedStep for IDA ( Intel Dynamic Acceleration ). This speed step in real is at least half the BUS frequency higher than the highest normal speed step. It is the cpufreq driver that displays it only with 100MHz higher. How ever, this is just a matter of displaying.

IDA is a feature of newer Core 2 CPU's ( I think it was the 7700 that introduced this ) and allows the CPU to overclock itself if all parameters ( temperature , workload, etc ) allow this. It only overclocks one Core and only if it is useful ( for example a single-thread application needs full power ).

Emme
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Re: Two highest speeds on Core 2 Duo

Post by Emme » Sat 28. Nov 2009, 19:09

Thanks for the clarification. That explains why this IDA state needs a higher voltage despite the wrongly displayed difference of only 10MHz.

sinter
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Re: Two highest speeds on Core 2 Duo

Post by sinter » Sat 13. Feb 2010, 19:01

I want to add that IDA and SLFM aren't new features at all. I have a T5470 cpu from june 2007 and it has both IDA and SLFM.

Besides this I think IDA frequencies should be disabled for power saving, because they need an unproportionally large voltage bump over the next highest frequency.

Emme
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Re: Two highest speeds on Core 2 Duo

Post by Emme » Sat 13. Feb 2010, 19:23

I don't think so, if IDA kicks AFAIK the other core is temporary disabled and consumes much less power.

on my C2D P8600, I run with these values since several months now:
R=V
1: V=26 24 18 17 T=0
0: V=26 24 18 17 T=0

So the IDA mode only has a little bit more power set than the HFM.
I consider SLFM only as "marketing bla", it is just the lowest frequency available (the FSB frequency).

sinter
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Re: Two highest speeds on Core 2 Duo

Post by sinter » Sat 13. Feb 2010, 19:31

This might differ between CPUs, because my T5470 gets significantly hotter with the IDA FID enabled (there is a 6C difference actually while watching youtube). I must add that my cpu needs 30 VID for IDA and 15 for the next best thing, but mine is an old 65nm Merom, so that might be the problem.

Gillian00
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Re: Two highest speeds on Core 2 Duo

Post by Gillian00 » Sun 14. Feb 2010, 13:50

with T8300, this 2.41GHz freq need higher voltage also and freeze each time if higher voltage is not set

gordan
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Re: Two highest speeds on Core 2 Duo

Post by gordan » Thu 27. May 2010, 14:35

Are the IDA FIDs/VIDs settable/forceable via phc?

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