I assumed you were referring to the physical slot (you only have a 4x physical slot). Assuming that is the case, then an adapter will work. If you have the physical slot size, but it run at 1x (or something below optimal) it will also work. Both cases, the result is that you lose bandwidth. Here's an example - http://www.cryptocables.com/wp-content/uploads/2013/04/1x.jpg (just something I found, not saying buy this one or from this vendor).