I have a Gigabyte M57SLI-S4 AM2 NFORCE 570 motherboard in my PC, which to my understanding can have a max of 4gb of RAM. Currently I have 2gb of RAM and I was wondering, if I were to upgrade, can I just add 1gb at a time, or do I need to add 2? I guess the reason I'm confused is that in the old days you couldn't add 128mb if you already had 256mb (for example), but you had to add it in doubles (or at least that's what I remember being told....)