What is a Jumper?

Definition of a Jumper & What They're Used For

A picture of a 2-pin jumper on a motherboard
2-pin Jumper on a Motherboard.

A jumper is a removable wire or small plastic or metal plug whose absence or placement on a piece of hardware determines how the hardware is to be configured. It works by opening or closing part of a circuit.

For example, if a jumper on a hard drive is in "Position A" (I made this up), it may mean that the hard drive is to be the master hard drive on the system. If the jumper is in "Position B" it may mean that the hard drive is to be the slave hard drive in the computer.

Jumpers have all but replaced an older hardware configuration mechanism called a DIP switch. Even jumpers are rare on most newer hardware today because of automatic configurations and software-controlled settings.

Important Facts About Jumpers

The device you're changing the jumpers on should be powered down. With the device on, it's too easy to accidentally touch other pieces of metal or wires that may then result in damages or unwanted changes to the device's configuration.

Tip: Just like when dealing with other internal computer components, it's also always important to wear an anti-static wrist strap or some other electric discharge equipment to prevent transferring electricity to the components, which can damage them.

When a jumper is considered "on," it means that it's covering at least two pins. A jumper that's "off" is attached to only one pin. An "open jumper" is when none of the pins are covered with a jumper.

You can usually just use your fingers to adjust a jumper, but needle-nose pliers are often a better alternative.

Common Uses for Jumpers

In addition to computer hardware like a hard drive, a jumper can be used in other devices too like modems and sound cards.

Another example is in some garage door remotes.

Those types of remotes have to have jumpers in the same positions as the jumpers in the garage door receiver. If even one jumper is missing or misplaced, the remote won't understand how to communicate with the garage door. Similar is a ceiling fan remote.

With these types of remotes, changing where the jumpers are usually adjusts the frequency of the remote so that it can reach the device that's listening on the same frequency.

More Information on Jumpers

The biggest benefit of using jumpers is that a device's settings can be changed only with a physical change of the position of the jumper. The alternative is that firmware changes the settings, which makes the hardware less likely to always comply because firmware is easily affected by software changes like unintentional glitches.

Sometimes, after installing a second IDE/ATA hard drive, you may notice that the hard drive won't work unless the jumper is configured correctly. You can usually move the jumper between two pins that will make it a slave drive or master drive - another option is moving it to cable select.

Older computers might use jumpers to reset BIOS settings, clear CMOS information, or even set the speed of the CPU.

A group of multiple jumper pins that are collected together is often called a jumper block.

Plug and Play eliminates the need to adjust jumpers on a device. However, some devices do come with instructions for manipulating the jumpers if you want to customize the settings - it's just not required like it is with lots of old hardware.