Does the nVidia GeForce 450 GTS take 2 PCI Express slots OR 1?

I want to buy an nVidia GTS 450, but i want to make sure my computer can handle it. I have only ONE free PCI Express slot currently. I heard somewhere that the nVidia 450 GTS is dual. Does that mean it takes 2 slots or 1? http://bit.ly/mjevps