Memory Upgrade
I have an iMac with four memory slots. Two slot have 2G DIMMs and the other two are open. Can I add two 4G DIMMs to the open slots without causing any issues or do all the DIMMs need to be the same size
iMac, OS X Mavericks (10.9.1)
Without knowing exactly what model iMac you own answering that question is difficult at best. Please navigate to Crucial.com or to OWC (www.macsales.com) who are both reliable RAM resellers. Both places can assist you with choosing the correct RAM for your machine and OWC even has install videos for your year and model iMac whatever it might be.