When you add a device to your computer, such as a new disk drive, you have to add it to the motherboard. This is done by plugging it into one of the expansion slots on the motherboard (usually there are several, since manufacturers know we love to buy new toys for our computers). Some motherboards can only handle certain CPU speeds, so if you're considering upgrading, you may need a new motherboard. (To find out how the motherboard works in relation to the rest of your computer, go to our illustrated Computer Tour)