Does the computer keeps using RAM when the computer is on, because I remember when I restart a computer or shutdown a computer, then when it starts, I remember i have about 350/512 free space, now after i've been on for about almost a day or a long time, it drops to around 230-250 and who knows? It may drop even lower. My question is, is this normal for computers? I'm total noob at RAMS. Please explain!