I have a 2.2 GHz SR MBP with the stock 2GB memory. I wanted to know if this is 2 x 1GB sticks in 2 slots, or 1 x 2GB stick in 1 slot. The reason I am asking this is I am interested in upping the total RAM to 4GB, but need to know whether I can just get 1 2GB stick to top it up, or I have to buy 2x 2GB sticks. Thanks.