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. Next to the pins is a silkscreen description of each of the pin settings. In the picture jump pins 1-2 for Normal mode, 2-3 for config mode, and when open the computer is 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 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. Also, whenever working in a computer or with any electronic device be aware of ESD.
How many jumpers are on a motherboard?
Every computer motherboard is different, which means there is no way to know how many jumpers are on a motherboard, unless you know the motherboard's manufacturer and model number. Once this information is known, this question can be answered by consulting the motherboard's documentation.