Does Turbo Boost cause a voltage jump when up-clocking on i5's?

[BSim500]

I'm thinking of buying a cheap i5 3470 for a HTPC build. I'm not interested in OCing beyond 4GHz as the focus is on a balance between a mild overclock and low heat & noise. Its base clock is 3.2Ghz but with the +4 bins limited overclocking + Turbo Boost, it would potentially have an OC of 3.8GHz (4 cores loaded), 3.9GHz (3 cores loaded) or 4.0GHz (1-2 cores loaded), which is just about perfect for my needs. Obviously it will need Turbo Boost enabled to do this.

Question : I have no i5 or experience with Turbo Boost, and have read a couple of comments that say enabling Turbo Boost causes the voltage to auto-increase (even when it isn't needed) as part of the Turbo Boost's auto-overclock feature. Obviously this is bad news for a HTPC.

Can anyone with an i5 at stock confirm in CPU-Z the difference in voltage behavior between TB enabled vs disabled under load. I mean - If I have a 1.15v stock chip that's also more than capable of hitting 4Ghz at same 1.15v voltage, I really don't want it to jump up to 1.25v as part of Turbo Boost's "feature", and I'd really like to know if this is how Turbo Boost works before I buy the chip.

Thanks in advance.

 

[Ed1]

the voltage is tied the the multiplier so yes as it goes to a higher speed so does the voltage .
for example say your idling at 1600 the voltage be like 0.950 , then it will max out like 1.050 .

thats just a example each chip will vary on actual number , this is of course with voltage set on auto .
you can generally lower the voltage a bit at low OC (below 4.0-4.2) using offset method .
If you set voltage to manual , then it won't change other than Vdroop which may happen under load .

 

[Sheep221]

From what I know, the turbo boost doesn't work when you overclock the CPU anyhow. It basically won't get triggered when you alter the frequency, so you just can max OC it to 4GHz manually, count 4 bins as turbo reserve and another 4 bins allowed on locked CPU. Or you will turn turbo boost into regular P-states.

 

[Ed1]

From what I know, the turbo boost doesn't work when you overclock the CPU anyhow. It basically won't get triggered when you alter the frequency, so you just can max OC it to 4GHz manually, count 4 bins as turbo reserve and another 4 bins allowed on locked CPU. Or you will turn turbo boost into regular P-states.

Depending on bios settings you can OC and set CPU multiplier in the CPU management section and this will disable TB .
But you can also set the TB multipliers (each core separate) in Asus MB its under AI tweaker , that is how I have mine set, staggered speed per core . Other MB will call it something else .

 

[BSim500]

Thanks very much for your replies.

Ed1 - "for example say your idling at 1600 the voltage be like 0.950 , then it will max out like 1.050."

Ed1, did you mean just in SpeedStep or Turbo Boost as well? I'm referring to comments I've read about a secondary jump that occurs with Turbo Boost. Eg:-

0.95v idle (Speedstep controlled) -> 1.15v (stock voltage) -> 1.25v (possible automated Turbo Boost voltage increase (if that's what happens))?

Ed1 - thats just a example each chip will vary on actual number , this is of course with voltage set on auto . you can generally lower the voltage a bit at low OC (below 4.0-4.2) using offset method .

Does any Turbo Boost change override offset, or will the offset override TB? Eg, if I set an offset of say -0.005v (taking it down to 1.145v on a 1.15v chip and not on "auto" anymore), would TB still cause it to jump to say 1.245/1.25v (if that's what happens) or will it stick at 1.145v, ie, does TB affect only frequency / multiplier and not voltage as well?

Ed1 - If you set voltage to manual , then it won't change other than Vdroop which may happen under load .

From what I understand, a "hard" manual (non-offset) unfortunately disables the lower SpeedStep 0.9v idle state voltage too?

Sheep221 - From what I know, the turbo boost doesn't work when you overclock the CPU anyhow

I know that's true on "K" chips above 4GHz (where the multiplier is set above the highest TB mode), but from what I understand the +4-bins OC won't work on non-"K" chips with TB disabled? I could be wrong, but I don't have an i5 to test it for sure.

Sorry for all the questions, but I have no access to an i5 to test these things myself, and I can't find the information anywhere though. I basically just wanted to know if enabling Turbo Boost changes just the frequency, or if it also ups the voltage over and above normal stock voltage as well as the frequency. If it does add say +0.1v on, then the heat isn't worth the TB-based overclock (in my experience "auto-overvolt" features tend to way overdo it and run much hotter than is needed). And if it doesn't change the voltage, then I'll instantly gain an extra 800MHz on a cheap non-"K" chip at stock voltage, which would be great.

If anyone has a non-"K" i5 chip (or even a non-overclocked i5 "K" chip) and has tested Turbo Boost vs non Turbo Boost, it would be great if you could give a rough idea of how much the voltage changes (if at all)? Thanks.