The computer case is a very important part of the computer. It protects all of the electronic components inside and provides adequate ventilation to prevent overheating. The case also should be capable of allowing you to expand your hardware if the need arises. Some cases only have 5 or 6 expansion bays. This may not be enough if you plan to add several drives. There also should be plenty of expansion slots on the back for adding AGP, ISA, PCI, PCIe, or other expansion cards. There are currently two basic types of cases for two different types of motherboards. The ATX case is shown above. It is for the ATX type motherboard and is the one most commonly used today. There is also a microATX case that is used with the slightly smaller microATX motherboard. Before the ATX case, there was an AT case for the older AT type motherboards. Many cases are made so that ATX, microATX, and even the older AT type motherboards will work in them. There are also several different sizes of cases. The larger cases have more expansion bays than the smaller cases have. The smallest case is the "desktop" type that lies flat. The next size up is the "mini tower," then the "mid tower," then the "full tower," and finally the "server," which is the largest. The server case is primarily used for server computers in businesses. The ATX mid tower case is the most widely sold case for personal use.