Computer tower

In personal computing, a tower unit, or simply a tower, is a form factor of desktop computer case whose height is much greater than its width, thus having the appearance of an upstanding tower block, as opposed to a traditional "pizza box" computer case whose width is greater than its height and appears lying flat.

Compared to a pizza box case, the tower tends to be larger and offers more potential for internal volume for the same desk area occupied, and therefore allows more hardware installation and theoretically better airflow for cooling. Multiple size subclasses of the tower form factor have been established to differentiate their varying sizes, including full-tower, mid-tower, midi-tower, mini-tower, and deskside; these classifications are however nebulously defined and inconsistently applied by different manufacturers.

Although the traditional layout for a tower system is to have the case placed on top of the desk alongside the monitor and other peripherals, a far more common configuration is to place the case on the floor below the desk or in an under-desk compartment, in order to free up desktop space for other items. Computer systems housed in the horizontal "pizza box" form factor—once popularized by the IBM PC in the 1980s but fallen out of mass use since the late 1990s—have been given the term desktops to contrast them with towers that are often situated under the desk.

Tower cases are often categorized as mini-tower, midi-tower, mid-tower, full-tower, and deskside. The terms are subjective and inconsistently defined by different manufacturers.

Full-tower cases, typically 20 inches (51 cm) or more in height, are designed for maximum scalability. For case modding enthusiasts and gamers wanting to play the most technically challenging video games, the full-tower case also makes for an ideal gaming PC case because of their ability to accommodate extensive water cooling setups and larger case fans. Traditionally, full-tower systems had between four and six externally accessible half-height 5.25-inch drive bays and up to ten 3.5-inch drive bays. Some full-tower cases included locking side-doors and other physical security features to prevent theft of the discs inside those bays. However, as modern computing technology has moved away from mechanical hard drives and optical drives toward solid-state devices such as USB flash drives, solid-state drives (SSDs), large-capacity external storage, and cloud storage, such an abundance of internal and external drive bays is less common. More recent full-tower cases instead only have one or two external drive bays, or none at all, with the internal bays moved elsewhere in the case to free up room and improve airflow.

Full-tower cases readily fit full-size ATX motherboards but may also accommodate smaller microATX motherboards due to the former standard's interoperability in mounting holes. Full-tower cases may also have increased dimensional depth and length over their shorter counterparts, allowing them to accommodate Extended ATX motherboards, larger graphics cards and heat sinks. Since the 2010s, full-tower cases are commonly used by enthusiasts as showpiece cases with custom water cooling, RGB LED lighting, and tempered glass or acrylics side panel. They may also hold two motherboards (as is the case with the Corsair 1000D) and dual power supplies (Corsair 900D).

Mid-tower cases, usually between 16 inches (41 cm) and 20 inches (51 cm) in height, are the most common form factor of personal computer towers. Before the late 2010s, mid-towers contained between three and four 5.25-inch drive bays and an equivalent number of 3.5-inch bays to house optical disc drives, floppy disk drives and hard disk drives, leaving just enough room for a standard ATX motherboard and power supply unit. Since the widespread adoption of USB flash drives, solid-state drives (which take up far less space than spinning hard disk drives) and the declining usage of internal optical drives, the number of drive bays has become less of a concern to the contemporary computer user, the internal space of mid-towers is now used more commonly for closed-loop water coolers, dual graphics cards, and tightly stacked SSDs.

The marketing term midi-tower sometimes refers to cases smaller than a mid-tower but still larger than a mini-tower (see below), typically with two to three external bays. Other times the term may be synonymous with mid-tower.