In an effort to upgrade my iMac to play Sky Rim, I made a dash to Fry's the local electronics sotre here in California. I bought a 4 GB SODIMM 667mhz stick of RAM. It put me back about $67 after tax. Installed and booted no problem. Then hours later I noticed my browser dumping my pages every 5-10 minutes and the OS completely freezing up so it needed to be rebooted. Clicking the Apple at the top left and selecting About this Mac, it show there to be 6gb total installed. The other slot already had a 2gb chip. I decided to pull my 4gb and replace it with another 2gb. Reset the computer and the OS has been running smoothly ever since. Which makes me ask, Is this a software or firmware restriction of RAM capacity? Suppose the only other future upgrade would be replacing the hard drive disk for a solid state drive. Interesting side note- there's a drawing beneath the pedestal that illustrates the procedure for upgrading or replacing your RAM just in case you forgot.