I have recently run into problems maxing out my memory usage. I am currently using 2x2gb sticks, and I have an extra 1x4gb stick. I don't have the specs/brands of them handy, but how would I go about checking if this 4gb stick is compatible with my motherboard? Is it bad to have different sizes or brands or speeds of RAM in a machine?
All three of those are bad, generally speaking. I'm not sure the system will even boot with sticks of different capacities, but if it does it won't run dual channel, so it'll likely slow things down.