Bit

In both main and secondary memory, information is stored as patterns of bits. Recall from chapter two what a bit is:

A bit is a single on/off value. Only these two values are possible.

The two values may go by different names, such as true/false, or 1/0. There are many ways in which a bit can be implemented. For example a bit could be implemented as:

• A mechanical electrical switch (like a light switch.)
• Voltage on a wire.
• A single transistor (used in main memory).
• A tiny part of the surface of a magnetic disk.
• A tiny part of the surface of a magnetic tape.
• A hole punched in a card.
• A tiny part of the light-reflecting surface of a CD.
• Part of a radio signal.
• Many, many more ways

So the particular implementation of bits is different in main memory and secondary memory, but logically, both types of memory store bits.