A desktop computer (often abbreviated desktop) is a personal computer designed for regular use at a stationary location on or near a desk (as opposed to a portable computer) due to its size and power requirements. The most common configuration has a case that houses the power supply, motherboard (a printed circuit board with a microprocessor as the central processing unit, memory, bus, certain peripherals and other electronic components), disk storage (usually one or more hard disk drives, solid state drives, optical disc drives, and in early models a floppy disk drive); a keyboard and mouse for input; and a monitor, speakers, and, often, a printer for output. The case may be oriented horizontally or vertically and placed either underneath, beside, or on top of a desk.
Personal computers with their cases oriented vertically are referred to as towers. As the majority of cases offered since the mid-1990s are in this form factor, the term desktop (or pizza box, for compact models) has been retronymically used to refer to modern cases offered in the traditional horizontal orientation.
Prior to the widespread use of microprocessors, a computer that could fit on a desk was considered remarkably small; the type of computers most commonly used were minicomputers, which, despite the name, were rather large and were "mini" only compared to the so-called "big iron". Early computers, and later the general purpose high throughput «mainframes», took up the space of a whole room. Minicomputers, on the contrary, generally fit into one or a few refrigerator-sized racks, or, for the few smaller ones, built into a fairly large desk, not put on top of it.
It was not until the 1970s when fully programmable computers appeared that could fit entirely on top of a desk. 1970 saw the introduction of the Datapoint 2200, a "smart" computer terminal complete with keyboard and monitor, was designed to connect with a mainframe computer but that did not stop owners from using its built-in computational abilities as a stand-alone desktop computer.