Most desktop PCs sold today are built in the tower form. A computer tower is a metal chassis that holds all of the computer's components. Towers are vertically-oriented, and are generally placed on the floor, next to the desk where you use your computer. Computer towers are available in an enormous variety of sizes to suit every need.
Every computer tower has the same basic features. A tower will have enough room for a computer's motherboard, which houses the CPU and any expansion cards, a hard drive and optical or disk drive and a power supply. Most towers, however, have enough room for more expansion, and may hold several hard drives and more than one optical drive. Most computer cases are made from steel or aluminum, and may have plastic internal parts to make it easier to install hard drives and optical drives.
There are no universal standards for the size classifications that apply to computer towers, although "mini," "mid" and "full" are three of the most common terms used. Generally speaking, a mini tower will be about 14 inches tall, a mid tower will be approximately 18 inches tall and a full tower will be 20 inches tall or more. If you are building a computer, make sure that you buy a tower that will accommodate your motherboard. While most computer motherboards will fit into a mid or full tower without any problem, a mini tower usually requires a small motherboard. Buy a tower that will allow you to expand your computer in the future, as well. A mini tower may only have room for one to two hard drives, while a full tower will have room for six or more.
Computer towers are available with a wide array of specialized features for enthusiasts with specific requirements. For musicians, it is possible to buy a tower outfitted with noise absorbing foam and mounting brackets for large, slow-moving case fans. For gamers, a tower might have a clear window allowing the components of the computer to be displayed. It is even possible to buy hand-made wood computer towers, although these must be custom-ordered and can be quite expensive.
It is possible to purchase computer tower cases for as little as $15, but higher-quality models tend to cost $30 to $80 or more as of 2015. Examine a tower closely before buying it. Less expensive towers may be poorly machined and have dangerous sharp edges on the inside, and will usually be constructed from thin steel, allowing noise to easily escape from the machine.
Although the vertically-aligned tower form is the most popular, computer cases are available in many other designs, such as the desktop form, which is horizontal and designed to rest on a desk rather than the floor. Additionally, the Mini-ITX form factor is popular with users who prefer smaller computers. A Mini-ITX case measures just 9-by-7-by-11 inches or less, and generally only has sufficient room for a single hard drive and expansion card.