Hard disks, sometimes also called hard drives, are storage devices for the notebook. Unlike the computer's memory, hard drives are not within the circuitry of the computer and are not on the motherboard itself. There is one hard disk within every single notebook computer! They are used to store large amounts of information. The data stored in a hard disk will not be erased when the notebook is turned off, unlike the data stored in the notebook's random-access memory (RAM). When the central processing unit of a notebook needs to use information stored on the hard disk, the data will be copied from the hard disk to the notebook's RAM. This is so a notebook can permanently store large amounts of information and operate at fast speeds at the same time!

Modern hard disks can store anywhere between 3 and 60 gigabytes. One gigabyte is 1 billion bytes, and one byte is 8 bits. Bits are a single binary digit-a 1 or a 0. Eight of these bits combined equal one byte, and one byte is used to represent a single letter, number, punctuation mark, or another special character. Hard disks can be used to store any kind of information from text files to graphics to the instructions in a software application!