Underclocking a 3770k

[Hero9989]

I'm going to be starting a mITX build soon with an SG05 case so I want a CPU that uses as little power as possible. I'm looking at the i7 3770t at the moment since it only uses 45w but still has the 8 threads making it more versatile.

The 3770k doesn't cost that much more and will have a higher resell value when it comes to selling it further down the line.

So yeah, is it possible / does anyone have any experience with underclocking /undervolting a 3770k to the 2.5Ghz of the 3770T. Also would this lower the tdp allowing me to use a smaller cooler and slower fan lowering noise?

 

[wazza300]

you can set to the equivalent to the 3770t's multi,idk what that is? 32? and to underclock on cpu voltage you would use a negative offset for example -0.010v would take off 0.0100v from the cpu's voltage and so on

the less work/speed/voltage it does the cooler it will run

 

[Rooster212]

Just put the CPU multiplier in the BIOS down to 20x or so? Auto volts should sort the rest? Don't forget Speedstep makes the processor step down in multiplier to 16x when it doesn't need to be at 34x or 38x or whatever clock it is at.

I don't know whether you would need a Z77 motherboard for this or not... it is hard to find people who underclock with a 3770K, can't really find any!

 

[Hero9989]

So it's that easy? The price difference between the 3770k and the 3770t isn't that much so if I could do it myself with the 3770k and keep the resale value that the k has over the t; much much preferred.

I was looking at a z77 motherboard anyway so that shouldn't be an issue.

I assume I shouldn't come into any stability problems with underclocking the CPU?

 

[stuie]

It under clocks itself on idle anyway mine shows as using 9 watts on idle in cpuz

 

[joeyjojo]

I'm going to be starting a mITX build soon with an SG05 case so I want a CPU that uses as little power as possible. I'm looking at the i7 3770t at the moment since it only uses 45w but still has the 8 threads making it more versatile.

The TDP doesn't actually tell you much, it's more of an upper limit. I would imagine most 3770K's are closer to 45 W than 77 W.

So yeah, is it possible / does anyone have any experience with underclocking /undervolting a 3770k to the 2.5Ghz of the 3770T. Also would this lower the tdp allowing me to use a smaller cooler and slower fan lowering noise?

If I was you I'd go for the K and see how it performs with your choice of cooler. You might find that it works fine. If it's too loud then you can always underclock it a few multiplier steps and undervolt.

 

[accod]

You could just limit the cpu in the OS so it can't go above X GHz. That way it will remain cool and quiet, and you have the option of easily removing the limit should you need to do something that needs more speed.

 

[Hero9989]

I remembered I have a 2500k processor in my PC so I actually did a couple of tests. This won't be totally indicative of the ivybridge equivilent but it should be close.

http://imgur.com/a/020au
The top image is at 2.4Ghz and turbo disabled
The bottom image is everything at default - 3.4Ghz with 3.7Ghz turbo
In both cases prime95 is running. Massive 45w difference with 1.3Ghz and a drop in temperature of 17 degrees C.

@joeyjojo - you are right, the TDP is the maximum amount of watts the package is allowed to produce - in the case of my 2500k its TDP is 95w but even with prime95 running (albeit for not very long) with the iGPU disabled it was only pulling 83w.
Saying that though - the power and temperature readings speak for themselves. I didn't test performance difference which is something I should really do - I'd have thought it was pretty linear though. There's no way to know how this will compare to an i7 with 8 threads.


I think it's pretty much a given now - With such good results - seems like I'd be stupid to go for the 3770T - losing resale value and expandability for very little monetary savings.
I'm going with the 3770k with the default clock set to 2.5Ghz (same as the 3770T) with the turbo set at 3Ghz. Obviously I'll do tests when I get the system built to find a sweet spot but that's my starting point I think!

Thanks for the help guys!

 

[joeyjojo]

That's interesting, I'm surprised actually how close to its TDP it's running. Thanks for doing that.

It's also nice to see that it follows the theory quite closely. Here volts have gone from 1.09 -> 0.95 (87.2%) and clock speed from 3.4 -> 2.4 (70.6%) which would mean power dropping to 0.872*0.872*0.706 = 54%, or 45W, which is not far off the 39W estimated by the program.

If it were me I'd find a clock that runs everything I want it to smoothly (decoding HD video for example) and then reduce the volts manually and check stability. Undervolting has the most power savings as it's squared as above.

 

[Hero9989]

That's interesting, I'm surprised actually how close to its TDP it's running. Thanks for doing that.

It's also nice to see that it follows the theory quite closely. Here volts have gone from 1.09 -> 0.95 (87.2%) and clock speed from 3.4 -> 2.4 (70.6%) which would mean power dropping to 0.872*0.872*0.706 = 54%, or 45W, which is not far off the 39W estimated by the program.

If it were me I'd find a clock that runs everything I want it to smoothly (decoding HD video for example) and then reduce the volts manually and check stability. Undervolting has the most power savings as it's squared as above.

Remember the 83w is it running with an 8% turbo. Should be looking to take another 7w ish off that when it's running normally. So that's almost a 20w window before stock hits the TDP.

But yea that sounds like a plan. For me, gaming is what I want this for - basically using it like a games console connected to my 40" TV. Looking at reviews over the past couple of years - CPU hasn't been a bottleneck for a long while. In most games, I know I won't see much if any increase in performance even going from a 2500 to a 3770.
The extra threads in the CPU should help when multi core processing properly takes off with DX11 and when the new consoles start making use of their 8 x86 cores. Should also help on the occasions where I do find myself encoding video. All in all it'll be handy to have the extra performance of the 3770k on tap should I need it.

So yeah, I'll probably run a few CPU intensive game like civ5 and find a nice stable clock for FPS and see how low I can get the voltage at that clock. Lowering the voltage to get a good heat/performance balance seems to be quite common with ivybridge CPUs.