I have an asus m4a79xtd-evo and im thinking of getting some new ram. The motherboard says that if only two sticks of ram are being installed to put them in the channels closest to the processor ( i dont have the manual or board in front of me so idk colors or names) but due to my heatsink im afraid that some ram wont fit . So my question is, how large of a performance loss could i expect if i installed my ram only on the 2 secondary slots??
By looking at that motherboard, I can assume that it doesn't support Dual Channel mode by making the "1+3" or "2+4" combo (which is usually present on 99% of modern motherboards, that's why they paint them memory slots in different colors, btw), rather your motherboard supports it by "1+2" or "3+4" combo, or doesn't have Dual Channel support at all (which is highly unlikely to find these days, because that would be stupid).
If you have a very big CPU cooler (something like NH-D14, I presume?), try installing your memory in the two blue slots ("3" & "4"), I think it would work just fine at full performance rate.
Your motherboard have two black slots in a row ("1" & "2"), and two blue slots in a row ("3" & "4"), so I think what they did, is that way so your Dual Channel accessed by putting memory close together, or (probably not, but...who knows?) it's accessed by putting memory planks in the very center, making a "2+3" combo...which would be waaay too strange, IMHO.