Jumper (computing)

In electronics and particularly computing, a jumper is a two or more connecting points that can be conviently shorted together to setup or adjust an printed circuit board, such as a computer's motherboard.

Jumpers are arranged in groups called jumper blocks, each group having at least one pair of oontact points and often more. In general, each contact in a jumper block terminates in a small metal pin. An appropriately sized conductive sleeve called a shunt is slipped over the pins to complete the circuit. (In non-technical environments, shunts are very commonly but incorrectly called "jumpers".)

Jumper shunts are almost always metal, and are usually encased in a non-conductive block of plastic for convenience, and to avoid the risk that an unshielded shunt will accidently short out something critical (particularly if it is dropped onto a live circuit).

When a jumper shunt goes over two (or more) jumper pins, current is carried across, and the electronic equipment is thus instructed to activate certain settings acordingly. For example, computer CPU speed and voltage settings are often made by setting jumpers. Informally, technicians often call setting jumpers "strapping". To adjust the SCSI ID jumpers on a hard drive, for example is to "strap it up".

As a general rule, the early generations of any given technology have many jumpers, often laid out in a way that is badly documented and difficult to set correctly. As time goes by, the designers find ways to streamline and simplify the jumper layout. For example, a typical early model Intel 386 mainboard might have 30 or 40 jumper pairs, while the final production models typically had just a handful -- sometimes only one.

The recent trend has been to try to eliminate jumpers entirely from hardware devices, by the use of auto-configuration.