Sliding windows come in Single, Double, or Triple. A single slider will have two sashes and one sash operates either left or right. A double slider will have two sashes and both operate left and right creating ventilation from either side. This is a great option for Colorado as the weather can shift in a moments notice. You still have great ventilation.
A triple slider will have three sashes and the outer two sashes move inward. This is an ideal window for larger openings that you wish to have some extra ventilation.