Hi, Is it possible to buy a 3770K and underclock it so much the TDP goes below the 45W of the 3770T?

How does one underclock the CPU, in the BIOS?

I will run linux and passively cool the CPU with a scythe big shuriken without the fan.

So I think I changed my plans... now I'm going for 2100T and scythe kozuti... does anyone know how if that would work passively without case. Do you think the kozuti could dispense 30-35W via convection alone?

The CPU Voltage drops with the Ratio. The lower you set the CPU ratio in the bios, the lower is the voltage.

For example Dual-Core Sandy bridge has CPU package power consumption of 25 watts @ 2.5Ghz 1.05V under Prime95 Load.

Passive cooling should be possible in some cases, assuming it will never reach 25 watts.

Ok, thanks, but what is ratio? The frequency? And is a T processor basically just underclocked or are there other power saving hardware modifications?

What is Prime95 load?

So the scythe kozuti can only handle 25W in passive?

I disagree with most of the assumptions in the above messages. TDP is not an accurate measure of much.

With modern Intel chips, they all idle at around 4 watts.... (whether 4 cores or two). They automatically adjust their internal voltage when not under load.

The amount of wattage is more related to the amount of work they are doing than the power of the CPU.

Most computers spend most of their time operating at little more than idle. If you want to reduce wattage, you need to look at the mother board and other components.

If you want to go 100% passive (not a good idea) get something with some big fins. Using the Kozuti is just asking for trouble.

In my personal opinion, underclocking modern Intel chips is a sort of a horse and era buggy idea.

Ok, but how do you explain the different TDP then?

Of course I'm asking for trouble, but completely silent trouble...

A fanless computer will run hot. What CPU you can run fanless depends on what temperatures you're OK with.


It's underclocked and undervolted. These are two different things. Related but different.
We don't know for sure if any T CPU has other power saving features than the ones you could implement yourself. But it's clear that if the 2100T has any, they're not efficient. Other models might be different.

People keep forgetting that some boards can't undervolt. And you'll want an efficient board to run fanless. You can't just pick any board. So if the automatic undervolting of a T model is different than the automatic undervolting of a regular model, the T model will heat up less. But the difference might end up being insignificant anyway.

Short answer: until further evidence comes out, don't bother with T and S models. Underclock cheaper models instead.

It is the maximum heat that the CPU will generate. It appears, at least with the SB, that the actual real life TDP is less than the rated TDP.

It is sort of like how the video card companies warn you to use a 700 watt PSU when all you really need is a 250 to 350 watt PSU.

Prime95 is for stress testing.

In sandy bridge every CPU ratio(multiplier x 100= CPU frequency) has certain factory voltage (SVID) associated with it and for number of cores activated.
It adjusts CPU multiplier depending how much work needs to be done.

But you don't need to know that, just enter the bios. Set the cpu Ratio by typing whatever number and you get lower heat.

Ratio - SVID
16x 0.9907
17x 1.0057
18x 1.0208
19x 1.0358
20x 1.0458
21x 1.0608
22x 1.0758
23x 1.0908
24x 1.1058
25x 1.1208
26x 1.1359
27x 1.1509
28x 1.1659
29x 1.1809
30x 1.1959
31x 1.2109
32x 1.2260
33x 1.2410
34x 1.2660

2100T has limited multiplier so SVID stays low and therefore heat output.

I refrain from calling it TDP, it is heat or whatever the software/sensor is reporting.


I have underclocked Quad to 20x100= 2Ghz and disabled cores to Dual-core at resulting 1 Volt factory-undervolted on completely non-undervoltable board with passive BOX cooling and it operates at 9 watts light loads at 70C, but it tends to overheat slowly over time, 1 degree added every few minutes, hours and days into eternity under the same constant load. The box can't handle the prime 95 loads that result 19 watts of heat.

It is unknown how well that kozuti will dissipate 25 watts passive and how fast will it tend to overheat over time.

Hi rupy, what is it you're trying to achieve with fanless operation?
Someone here has a signature of "fanless is pointless!" I tend to agree with this, a single good fan run very slowly, 300~500rpm, will be pretty much inaudible in all circumstances and make cooling much, much easier and more effective than fanless.

SPCR built such a thing, a Single Moving Part PC, it's noise level is below SPCR's anechoic chamber!

This kind of PC will be large (ish), if you want a small quiet PC then look at the "heatsink cases" quite a few of which have been reviewed by SPCR. These generally only cool the CPU and you will need to use "on-board" graphics, in older systems built in to the motherboard chipset in newer ones it's in the CPU package.

If you want significant graphics power and passive operation that will be tough! For good fanless cooling size is key.
My PC is super quiet at idle, barely audible and has to be stressed hard before it increase it's noise level. Typically gaming isn't stressful enough, folding@home on CPU+GPU on the other hand gets it fairly excited, but it will pull 330w AC. Removing the CPU over-clock would help a lot.

Anyway what is it you want to achieve, if you want passive as a challenge or "for the sake of it" fair enough but if you just want a PC you can't hear you don't need a fanless one.

Hope helps, Seb

Thanks for all the useful info!

I have a completely silent Atom setup with PicoPSU and SSD now.

I want to play diablo 3 and other upcoming games so I need something beefier.

I think I'll have to go with the Ivy Bridge though... shame it's 45W, we'll see how the kozuti handles in open air... inside a case you can't passively cool anything, I totally agree...

@SebRad: Yes the Scythe Kozuti is COMPLETELY silent! It makes less noise than the electric buzzing of the hardware!

So I went for the 3770S, DH61DL, Streacom F1C and PicoPSU 90, it's awesome!

It's a tight fit, both for the Kozuti and the PicoPSU.