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Advice needed on i5 3470 Turbo boost OC

post #1 of 6
Thread Starter 
Hi all, first post here, and I could use some serious advice.

I'm thinking of buying a cheap i5 3470 for a HTPC build. I'm not interested in heavy 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 from what I understand, with the +4 bins limited overclocking + Turbo Boost, it would potentially have a max OC of 4.0GHz (3.6Ghz Max Turbo + 400Mhz), which is just about perfect for my needs (a 4GHz i5 at the lowest possible voltage). Being a non-"K" chip, it will need Turbo Boost enabled to do this.

Here's the question I just cannot find the answer to anywhere : Does Turbo Boost increase just the frequency or the voltage as well? I have no experience with i5's or Turbo Boost (currently have a 4.2GHz OC'd i3 530), 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 explain / confirm in CPU-Z the difference in voltage behavior between TB enabled at 3.8Ghz load vs disabled at 3.4Ghz 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 say 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, or how I can prevent "auto-over-volting".

Ideally, I'd like the 4Ghz at stock voltage, but I'm completely unaware of how Turbo Boost works. Does TB override the offset voltage - or does the offset override any TB increase? If I have a 1.15v chip and I enter say -0.005v (taking it down to 1.145v), will that voltage "stick" at 4GHz with TB on as it would at 3.2GHz with TB off? Will it also knock off -0.005v off of any TB's voltage increase? I still don't know for sure if TB does increase the voltage, as nearly all OC talk is about unlocked "K" chips. There's also a big unhelpful difference between reviews too. Eg:-

In this Anandtech review, a 3470 shows 3.991Ghz @ 1.128v...

... and yet in this HotHardware review, another 3470 shows a 4.028GHz at a whopping 1.328v?

I have an Asus P8Z77-M if it's of any use.

If anyone has a 3470 (or nearest) chip or even a 3570k still at stock, I'd be grateful if you could share your experience in voltage between TB on vs off. Thanks for any advice you can provide.
post #2 of 6
As long as your motherboard bios allows you to set an offset voltage or a fixed voltage then no worries. You can set your CPU voltage to whatever you want. The Asus P8Z77-M should have these features but have a look in the manual to make sure.

The only thing to worry about are motherboards that have limited bios options and no control over voltage. Computers you buy from big box stores often have very limited adjustments available in the bios. In this situation the CPU will request voltage (VID) and the motherboard will look at that request and give the CPU the appropriate amount of voltage, more or less. As the CPU goes faster and turbo boosts more and as the load increases, it will give the CPU more voltage. An adjustable bios lets you override this so you can control the voltage.
post #3 of 6
Hi, i have a i5 2400 on a Gigabyte z77-d3h.

First, the 40 multiplier x100 =4000mhz that you see is with a workload on 2 cores only!
Leaving the turbo enabled with the max multipliers available will give:
38 multi for 4 core workload.
39 " " 3 " " .
40 " " 2 " " .

You can still overclock slightly the baseclock:
ex: 103 x 38 = 3900Mhz on a 4 core workload.

You can also disable the turbo and put the max multiplier available for 4 cores = 38.


Voltage wise:

If you leave it on "auto", the processor will "ask" a certain voltage according to workload and multiplier.
This is the VID, you can see it with the prog "Core Temp".

You can see the real voltage applied on the processor in cpu-z. (Vcore)

The offset allow to decrease or increase of a certain amount the Vcore according to the VID.
With trial and error you can chose the best offset that will apply the minimum voltage needed according to the VID asked.


This way you keep the best performance available and also the power saving features.
post #4 of 6
Thread Starter 
Quote:
unclewebb - "As long as your motherboard bios allows you to set an offset voltage or a fixed voltage then no worries. You can set your CPU voltage to whatever you want. "

Thanks for your reply. The P8Z77-M does have both fixed & offset voltage adjustment. I don't want to use fixed voltage as from what I understand that disables the lower SpeedStep idle voltage? It does have a negative offset voltage option though (which seems to undervolt fine on a temporarily borrowed i3-3220) - but since I've no prior experience with Turbo Boost, I wasn't sure if negative offset would override the Turbo Voltage or if whatever voltage TB requested took priority. Thanks.
Quote:
robinaish - You can also disable the turbo and put the max multiplier available for 4 cores = 38.

Does that work with Turbo Boost disabled? I thought the +4 bins OC thing needed Turbo Boost enabled and that only "K" chips could set a higher multiplier manually without TB? I could be wrong - I simply don't have an i5 to test it with yet. Thanks for your post too, very helpful.
post #5 of 6
On my motherboard, i can do that.
But there is only inconveniences: you'll lose the 39 an 40 multipliers for 3 and 2 cores workload.
post #6 of 6
Thread Starter 
Quote:
"On my motherboard, i can do that. But there is only inconveniences: you'll lose the 39 an 40 multipliers for 3 and 2 cores workload."

I can live with that. I'm not too fussed about wringing the last Hz out of it under heavy load, I just wanted a nice 20% stock voltage OC (3.4GHz -> 4.0-4.1GHz) whilst keeping voltage & heat down under load.

Thanks very much for your help guys. Since it looks like I can easily compensate for any unwanted TB induced voltage jump with an equal negative voltage offset, I think I'll go for it. thumb.gif
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