PC Hardware in a Nutshell, 3rd Edition

Setting Jumpers and DIP switches

Jumpers and DIP switches are two methods commonly used to set hardware options on PCs and peripherals. Although they look different, jumpers and DIP switches perform the same function—allowing you to make or break a single electrical connection, which is used to configure one aspect of a component. Jumper or switch settings may specify such things as the amount of installed memory, the base address, IRQ, and DMA assigned to a device, whether a particular function is enabled or disabled, and so on.

Older PCs and expansion cards often contain dozens of these devices, and use them to set most or all configuration options. Newer PCs typically use fewer jumpers and DIP switches, and instead use the BIOS setup program to configure components. In fact, many recent motherboards (e.g., Intel Pentium 4 boards) have only one jumper. You close this jumper when you first install the board to allow such static options as the speed of the installed processor to be configured, or to perform such infrequent actions as updating the Flash BIOS. That jumper is then opened for routine operation.

More properly called a jumper block, a jumper is a small plastic block with embedded metal contacts that may be used to bridge two pins to form an electrical connection. When a jumper block bridges two pins, that connection is called on, closed, shorted, or enabled. When the jumper block is removed, that connection is called off, open, or disabled. The pins themselves are ...