Jumpers allow the computer to close an electrical circuit, allowing the electricity to flow certain sections of the circuit board. Jumpers consist of a set of small pins that can be covered with a small plastic box (jumper block) as shown in the illustration to the right. Below the illustration, is a picture of what the jumpers may look like on your motherboard. In this example, the jumper is the white block covering two of the three gold pins. Also, next to the pins is a silkscreen description of what the pins do, in this case when pins 1-2 are jumped the computer is operating normal, when 2-3 are jumped it is set into configuration mode, and when open the computer will be in recovery mode.
Jumpers are used to configure the settings for computer peripherals such as the motherboard, hard drives, modems, sound cards, and other components. For example, if your motherboard supported intrusion detection, a jumper can be set to enable or disable this feature.
In the past, before Plug-and-Play, jumpers were used to adjust device resources, such as changing what IRQ the device is using. Today, most users will not need to adjust any jumpers on their motherboard or expansion cards. Usually, you are most likely to encounter jumpers when installing a new drive, such as a hard drive. As can be seen in the picture below, ATA (IDE) hard drives have jumpers with three sets of two pins. Moving a jumper between each two pins will change the drive from master drive, slave drive, or cable select.
Tip: Some documentation may refer to setting the jumpers to on, off, closed, or open. When a jumper is on or covering at least two pins it is a closed jumper, when a jumper is off, is covering only one pin, or the pins have no jumper it is an open jumper.
Caution: When changing the jumpers on any device, the device and your computer needs to be turned off. In addition, whenever working in a computer or with any electronic device be aware of ESD.