I recently bought a new notebook which came with an integrated Intel HD 4000 graphic chipset and a standalone 2GB GT640M. The Nvidia control panel gives me the option to use the HD 4000 or GT640M as a "preferred graphic device". I can set this option per game (that is, per EXE-file) or I can set this option for everything running on my notebook. I don't quite get it, why would I ever want to have the low-end HD 4000 to render and process graphics instead of the much faster and more capable GT640M? Because the screen is connected to the bus of the HD 4000 I cannot turn it off, otherwise I'd turn off the onboard chip completely.

If they did it right, using the HD4000 will consume less power (when you use it, the GT640 is OFF). Less power is normally a big deal for a notebook translating to more hours between recharges.

So, a possible way to use the two graphics units is: Use the HD4000 for most non-game activities -- e.g. surfing, running a spreadsheet. Use the GT640 for games and, perhaps, video (sometimes video is optimized for the better graphics unit -- try and see if there is a difference).

HD4000 drivers are from Intel. Intel is noted for "poor to fair" drivers -- sometimes they don't work at all with some types of application (though they claim to be improving). So, one might also find that some stuff just does not run right on the HD4000. In that case, use the GT640 (Nvidia writes excellent drivers, normally).

This is all general info/opinion gleaned from many articles over the months/years -- as I do not own an HD4000 containing CPU (i.e. recent Intel CPU) -- so cannot speak directly about it. BTW, the HD4000 is part of the CPU -- not a separate chip.

FWIW

So when power is not an issue, there's no other possible advantage of having the HD4000 selected as processing unit for graphics over the GT640M.

nope,

the 640 should be the dedicated GPU for Games, HD4000 for Desktop, HD4000 should also be capable of Decent Video decoding (DVD, Youtube, etc).

HD4000 uses a lot less power than the GT640 does in desktop and idle situations

The Intel chip will create less heat too.

Thanks for clearing this up.

with HD4000 Disabled, the CPU will run cooler during gaming, with it Enabled for Games, you'll set your laptop stand on fire.

on the desktop, with the GT640 disabled, the entire system will run cooler than it would if the 640 was running all the time.

at least using the 640 GPU, the card is away from the CPU. dividing the heat between 2 different sources is better than having it all built up in 1.

The notebook is used as a desktop without the battery in it and heat is not a problem either.

I was thinking that enabling the HD 4000 would add some cumulative performance or whatsoever but since that's not the case, it's GT640 all the way.

nope, you cant Run an 4000 and 640GTXM in SLi.. lol.

But... if it was an AMD CPU, you can run the APU GPU Core and Addin Card in XFire... lol