I would like to underclock my eVGA GeForce 8800GT 512 MB when I am not gaming. It can idle at 59 C on a hot summer day. Since it's not being fully utilized with non-gaming / HD video viewing, I'd like to cool it down. The current default settings in Rivatuner show:

• core: 600 MHz
• shader: 1500 MHz
• memory: 900 MHz

My question is how much should each of these numbers be decreased? Are there set rules or optimal numbers? I'd still like my dual 22'' + 17'' displays to not lag. These screens didn't even lag much when I had an ATI Radeon X300 with Vista.

well you could probably downclock it 50 % or so... but you'd have to do it manually each time unless you use ntune (which sucks)

I use evga precision though... even though it doesn't have all the features of riva, its much cleaner

I do this to my 8800GTS 640.
Use RivaTuner to turn the core/mem clocks to it's minimum.
Save it as a new profile and have it apply these clocks on startup.
When you want to game, open RivaTuner and switch the clocks back to stock or even a little higher.
It will not let you take it to low so no worries there.
260 core and mid four hundreds for the memory is as low as it lets me go.
I know from previous testing with Ati Tool's settings that my card was still stable at 125 core and mem.

I don't understand what those 3 numbers mean and which one contributes mostly to the temperature. Do all 3 numbers have to be lowered by the same percentage for stability?

Do I also need to lower voltage when I underclock?

I lowered everything by 200 MHz. There was only a 1 C drop in core temperature. Am I doing something wrong? Do I have to lower wattage / voltage somehow?



I then dropped everything to the lowest it would allow me (half of stock). Once again, I only saw a 1 C drop in temp. Edit: after waiting 15 minutes, it dropped another 1 C.

Nahh
Same with mine.
Half clock speed gets me ~2c temp savings.
GPU's are designed to run hot so I am not to worried, more for the energy savings then the heat. Try turning the fan up as far as you can stand it. If that dose not help enough, remove the cooler and replace the thermal goo with some AS5 or better.

As far as I know, there is no easy to lower your voltage. You could try editing the BIOS but that could be troublesome.

Will halving all the frequencies halve the wattage? I'm skeptical about the power benefits of underclocking, because it seems that power and heat are closely related. If my temperature only dropped 3 C, then I don't think the power usage dropped much either.

And if you slow down the GPU, will programs put more strain on the CPU? Will the operating system know that if the GPU is slowed down, then it should send relatively more instructions to the CPU?

No. It will lower it but I am not sure bye the exact amount. To help prove the point head over to the eXtreme Power Supply Calculator and give it a try. My G0 Q6600 @ 2.4Ghz, 1.25V draws 95W. At 3.6Ghz, 1.25V it draws 143W. If I drop it to 1.2Ghz (lowest my Mb will let it go, 6x200Mhz) at the same voltage it is at 48W. So, assuming the voltage dose not change from 1.25V, the total wattage used goes from 48W @ 1.2Ghz to 143W @ 3.6Ghz. Quite a drop for no change in voltage.

No, and no. GPU and CPU are completely separate no mater what nVidia wants you to think. Lowering your GPU clocks will slow down your FPS in gaming and drop your power consumption a little, nothing more.

If the temps don't drop, the power isn't dropping much either. Sounds like it probably isn't worth the effort. If you notice on CPUs, they drop frequency and voltage. I think voltage has the most affect. I've never messed with voltage on Gfx cards though (too scared). Doesn't your card have power saving features? I know my recent ATI cards do.

My card has no power saving features. I monitor all the stats, and they remain the same unless I manually change something or set up a scheduler.

So graphics instructions cannot be run by CPU's? What if you have integrated graphics that can't do squat? Isn't the CPU forced to do more?

How about increasing the fan speed if temps are your concern (and noise isn't)? You'll see a much more marked drop in your temps with that as opposed to reducing clock speed.