A bit is a single binary character. it is either a zero or a one. This is because data is stored in a "yes/no" format. On a magnetic drive, a point it magnetized as north or south. If it is recorded as north, this means 0, if South, then 1. In all other cases, a pulse or change is a one. A lack of signal or change means a zero. Optical drives have the foil backing melted in points to make these ones—gaps are zeros. Flash memory uses physical switches, which are set to "yes" or "no" (one or zero) by electric impulses. As a computer works and "thinks," it sends pulses through its various systems for ones, and pauses for zeros.