Okay, I already searched the forum with no luck....I have checked Apple's website and the tech specs for my late '06 MBP with a 2.33GHz Core 2 Duo says the max RAM that my machine supports is 3GB. I was reading elsewhere on this site and discovered that there still was a benefit in running two matched 2GB DIMM's and so, after over a year of running 2 and 1 GB DIMM's, I installed a second 2 GB DIMM expecting to see a slight increase in my RAM number (I'd read where the MB actually recognized 3.3GB)...well, my machine is reading 4GB! Everything is running fine so far. EDIT: Found the answer by checking Activities Monitor: Show's 4GB as well but If I look over at Free, Active, Wired, etc...the "used memory" total added to the listed "free memory" adds up to 3GB of RAM. So 3GB it is.