externally accessible drive bays. The full tower case was originally developed to house file servers which would typically be tasked with serving data from expensive CD-ROM databases that held more data than the hard drives commonly available at the time. Hence, many full tower cases include locking doors and other physical security features to prevent theft of the discs. However, as computing technology moves from floppy disks and CD-ROMs to large capacity hard drives, USB flash drives, and network-based solutions, more recent full tower cases typically only have none, one, or two external bays for CD drives, with the internal bays moved elsewhere in the case to improve airflow. Today, full tower cases are commonly used by enthusiasts as showpiece display cases with custom water cooling, lighting, and tempered glass (replacing acrylic). They may also hold two computers (as is the case with the Corsair 1000D) and dual power supplies (Corsair 900D). Mid-tower cases are smaller, about high with two to four external bays. They may also hold two computers. A mini-tower case will typically have only one or two external bays. The marketing term midi-tower sometimes refers to cases smaller than mid-tower but larger than mini-tower, typically with two to three external bays. Other times the term may be synonymous with mid-tower. Layout Computer cases usually include sheet metal enclosures for a power supply unit and drive bays, as well as a rear panel that can accommodate peripheral connectors protruding from the motherboard and expansion slots. Most cases also have a power button or switch, a reset button, and LEDs to indicate power, hard drive activity, and network activity in some models. Some cases include built-in I/O ports (such as USB and headphone ports) on the front of the case. Such a case will also (normally) include the wires needed to connect these ports, switches, and indicators to the motherboard. Major component locations The motherboard is usually screwed to the case along its largest face, which could be the bottom or the side of the case depending on the form factor and orientation. Form factors such as ATX provide a back panel with cut-out holes to expose I/O ports provided by integrated peripherals, as well as expansion slots which may optionally expose additional ports provided by expansion cards. Many larger ATX cases can also be used with motherboards of other form factors. The power supply unit mounting point differs