I'm new to your excellent site and have both a general and a specific question. They may of course be based on faulty premises.
Can you turn a discrete graphics card off (using the BIOS or another method) when not doing graphics intensive tasks and just rely on the integrated graphics of the CPU? If you can, would that be an easy way to make a computer quieter since some graphics cards use as much power as a CPU (I'm assuming the graphics card's fan would also shut off)?
This basically how Nvidia Optimus
works, you can use Intel iGPU for all day working, and once an app that requires the use of the dedicated GPU it switches automatically (intel for nvidia), this is very transparent and with todays drivers it works very well, newer games you do have to add to the profile, or wait for new drivers so they are included. Sadly this hasnt reached desktops, and i kinda think it wont, in laptops its easier for manufacturers as they control all the hardware, firmware and bios, even their own designs of pcbs of mobos, cards, etc. So its easier for them to test and have a working finish product, while in desktops there are so many options in hardware that its impossible to control it. AMD also has their manual GPU switching, but all of this is also meant to save battery in laptops and not use a powerful GPU while not needing it.
I'm about to replace a 10-year-old Dell Dimension and want less noise (it was quite noisy, mainly the fans, even when new) as well as more speed. I'm going to stick with Windows for now (though I will probably buy a Mac Mini after its next upgrade to replace another old Dell--I've tried one and it's certainly quiet enough for me). I'm considering Dell's XPS 8700 (after all discounts, about $550 for one with an i7-4770, 8G of memory, and a 1T hard drive), which comes with either an AMD Radeon HD 7570 (standard) or an nVidea GeForce GTX 645 ($50 extra). Would I ever notice a performance difference if I'm not a gamer? I'm also considering skipping a discrete card altogether since the i7-4770 is supposed to have quite good integrated graphics. Also, I wonder which uses more power and therefore generates more heat, requiring more fan cooling. NVidea's site says the 645's max power usage is 130 watts, which is very high. I can't find the spec on AMD's site for the 7570 but another site says its max is 44 watts. If that's right, I'd guess the 8700 would be quieter with the AMD, unless the 645 has better power regulation when not at peak load.
If you are not gaming or have use for the cuda cores, just use intels built in iGPU, it should be enough for almost anything the average user needs, even playing 1080p is easy for the built in gpu. The only reason to go for a dedicated GPU is if you plan on gaming or if you have apps like cad that can take the advantage of the cuda cores.
With that said, nvidia has been really good designing their cards so they can downclock a lot when they are not bieng stressed, here is a picture of my GTX580
There are cards that i have read can stop their fans if the conditions permits, like for example read this review, GURU3D MSI GeForce GTX 760 Gaming review
The idle results are brilliant, the fan will even turn itself off when the GPU idles.
Btw dont get a dell, if you can built it, its not that hard and you can chose the components that will give you better performance and less noisy. Dell uses a lot of proprietary hardware that you cant easily replace, imo not worth it, unless you do value their support.