In the picture above you can see that there are a lot of openings on the back of a computer case. About halfway down on the left, is where the motherboard's input and output ports are located when installed. In the top left-hand corner you can see where the power cord plugs in from the wall outlet. Below that is the main power supply on/off switch. Barely visible, between the two, is a small switch that allows you to select different voltage types for different countries. Many parts of Europe, as well as other countries, use different electrical voltages than those used in the U.S. The larger circular shaped holes to the right cover the fan for the power supply. This fan not only cools the power supply, but it also helps cool the inside of the case as well. The small holes down the right side provide increased ventilation for the case. There is also a location for a second optional case fan behind the bottom half of these holes. Near the bottom, on the left-hand side of the case rear panel, are seven expansion slot covers. These covers can be removed to connect an AGP video card, PCIe cards, PCI cards, or any other type of expansion cards that might need to be installed in one of these openings.