Hi, I have a iMac 2.5Hgz Intel Core i5 4 GB 1333 Mhz DDR3 I want to expand to 8GB. As far as I know, I have 2 free slots available on my mac. So I would like to buy 2 modules, 2GB each. Mac sells each memory module at 150 USD. Apparently. this is an alternative: http://www.provantage.com/kingston-technology-kta-mp1333-2g~7KIN9175.htm I would like to know if I can use the kingston memory and if I can combine it with the current mac memory modules already installed. If so, why the mac price is so high compared with kingston ? Thanks.