As the name implies, the traditional desktop case is made to sit horizontally on top of a desk. Normal height ranges from approximately 4.5 to 6 inches, depending on the manufacturer. Width and depth also vary, ranging from 16 to 18 inches, and 15 to 19 inches respectively. A tower case is taller than it is wide. It's basically a desktop case standing on its end with all the drives and boards rotated 90 degrees.
Towers take up less desktop space and are also easy to put under the desk.
Usually between 16 and 20 inches high, a mid-tower is roughly the same size as a traditional desktop case. Oversized tower These large cases reach up to 24 inches high and have much more space for boards and slots than a traditional desktop or full-tower case. ATX motherboards are shaped differently than the AT and baby AT boards commonly used today, and the back of the computer case has to be set up differently in order to accomodate the new shape. ATX-compatible cases make access even easier. These are the same size as regular full-tower cases, but are made specially to hold ATX motherboards.