Hi..I have an iMac 21.5 inch with Processor3.06GHz Intel Core 2 Duo and Memory 4GB 1067 MHz DDR3 . Now, I want to upgrade it to 8GB RAM. I think, the iMac has 4 slots. Right now, it has 2GB -2GB in 2 slots and 2 slots are vacant. Im thinking to buy this, http://www.memoryupgrade.pro/4gb-apple-imac-215-inch-306ghz-1066mhz-so-dimm.html Is it compatible with my iMac ? Let me know please.