I just bought a refurb 17" white iMac with the 1.83 GHz Core 2 Duo processor. It came with 512MB RAM in one slot with the other slot empty. Should I just add a matching 512 MB chip in the empty slot for a total of 1GB? Or does it not matter that the chips match and add a 1GB chip to the other slot for a total of 1.5 GB of RAM? If they must match does brand matter? Will I have to match the new chip exactly to the one that the Apple put in the machine or will any 512MB chip provide a match? Finally am I better off just removing the 512MB chip and replacing it with a 1GB? What is the best way to do this for maximum performance? Cost is not a big issue, I found that the RAM is really cheap. Thanks!