Is this possible - 2x4GB RAM chip?

This gets a bit confusing here sorry ;-{

So day one Apple specs out the max memory this system can support is 4 GB (two 2GB modules). As time moves forward memory manufactures are able to make denser chips 4 GB models are introduced. Now a few years later 3rd parties discover this system can in fact support one 4 GB module and one 2 GB module to create a total of 6 GB of RAM. The limits of the system hardware limit the system to this.

So the bottom line here is both answers are correct! Day one: 4GB (2-2GB) a few years later 6GB (1-2GB 1-4GB). But before you add the memory make sure your systems firmware is upto date. Follow this Apple T/N: About EFI and SMC firmware updates for Intel-based Mac computers.