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Does i5 Turbo Boost affect CPU voltage or just multiplier freq?

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a b à CPUs
June 7, 2013 10:31:50 AM

Hi, I'm thinking of building a HTPC with a 3470/3570 i5 CPU - it won't be pushed above 4Ghz (instead optimised for low heat & low fan noise, hence non "K" chip version). Ideally, I'd love to get a good 800MHz extra speed (3.2-3.4GHz base + 4-bins limited OC + Turbo Boost = 3.8-4.0GHz (4 cores loaded) / 3.9-4.1GHz (3 cores) / 4.0-4.2GHz (1-2 cores) depending on CPU.

Q. Is Turbo Boost constrained to whatever Offset Voltage you set (ie, if you have a default 1.15v chip, and it's capable of comfortably running 4.0-4.2GHz at same voltage, will switching Turbo Boost on, override that voltage when it kicks in, or does the TB feature only change multiplier frequencies and not voltage? I'm concerned about the effect of Turbo Boost over-compensating on the voltage (eg, 1.3v) making it run unnecessarily hotter than usual (unwanted in any HTPC).

Motherboard is Asus P87ZZ-M.

Thanks.

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a b à CPUs
June 7, 2013 11:05:03 AM

Turbo boost adjust the Voltage and ratio at the same time, putting an offset voltage will hurt temps and longevity as it'll add to the amount already added to reach higher clock...

You could fix a Vcore for high clock but it'll not return to low voltage when you're idling and compromise a little heat (but a low voltage will be better than an offset to high voltage)

PS: the only way to know how voltage TB add is to test it, grab CPU-z and try TB max Vcore read (not the real but unless your motherboard have Vcheck points like me, it's pretty much the only way) in load and at idle, then enable Turbo boost and redo the same test... I suggest Cinebench 11.5 to test as in advanced bench, it feature a single core and a multicore test.

Then you'll know (approx.) how much TB add for max clock and will put an offset to keep that working at higher clock but still without passing the danger zone...

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