Hi, I know it's "highly recommended" that I buy RAM in matching pairs. Many people give this advice, but I find that they don't know exactly why. Admittedly, I don't either. I have 2 x 512MB sticks of RAM (ordered it from Apple with my MacBook since it was actually cheaper to do it this way in Australia) and my machine chokes on such a small amount since I play with lots of photos. My old 12" PB only had 1.25 GB total, and it seemed to run fine, so I guess this need for RAM is a consequence of the new architecture or something. (I have around 500,000 page-outs in 11 days of uptime) I want to buy a 1GB stick of RAM, but don't have enough money for 2 x 1GB sticks. If I buy it, I'll have 1x 512MB stick, and a 1GB stick of RAM, for a total of 1.5 GB. I believe that the speed of my RAM will be slower if I have a mismatching pair installed, but will my machine still benefit from the increase? Will it run as if it only had 1.2-1.3 GB of RAM because of the resulting slowdown of my RAM performance? PS: I've done 3 searches of the entire board before starting this thread.