Look in you motherboard manual and will instruct you where to install one card and where to install 2 cards. Do it their way. To use two card you will need a quality power supply, room in the case and great cooling. If you went to User CP at the top of every page and filled in your (My System Specs) it would help us help you. One or two cards all depends on your needs, wants, and money to spend. 16x and 8x is your Google home work for tomorrow.