I recently purchased the entry level mid-2010 iMac which has 4GB of RAM. Reviews state it can be configured with a maximum of 8GB of RAM. EveryMac shows this system as capable of 16GB of RAM. Over the weekend I attempted to install two 4GB modules in addition to the two 2GB modules already present. The system would not boot and beeped with what I assume is a memory error diagnostic. I pulled the 2GB modules (for a total of 8GB) and received the same error. I then re-installed the original two 2GB modules and two additional 2GB modules and the system booted fine and shows 8GB of memory. My question is: Is this system really limited to 8GB as I have read (and therefore the information posted on EveryMac is in error) or are there certain modules which need to be used in the system to reach the 16GB or, more appropriately, the use of 4GB modules. The 4GB modules are of the rated speed for this system and therefore that should not be the issue.