Complete manual/41/en

Noise is the data that is created by either the manufacturing process that creates physical devices and hardware, or by how they physically move and operate, like how a disc spins in a hard drive. An example of noise is the common SD card that we use to record and store digital photographs in our cameras. Each SD card has unique ‘scratches’ that are produced by the machines that manufacture them, similar to a person's fingerprint ridges. These make microscopic changes that are not visible to the eye but can be recognised by computers.