A small, plastic-covered metal block that is pushed onto two pins to close a circuit. An alternative to the DIP switch, the jumper is a less costly on/off switch found on motherboards and peripheral devices for one-time configuration. Although jumpers exist on modern computers, especially on hard disk drives, they were more prevalent in the early days of personal computers. Configuration of the hardware via software eliminated the use of many jumpers. See DIP switch
Jumpers are used to select options on printed circuit boards. The more sophisticated the board, the fewer the jumpers. Having no jumpers is best if changes have to be made by the user, otherwise the board has to be pulled out of the case.
Hard Drive Selection
Jumpers are used on IDE/ATA hard drives to select their operation mode, and schematics like this one are commonly found on the drive to show how to place the jumper on the pins. In "Single" mode, the jumper is not used.