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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.
QUESTION 3:
(Thought question:) Does the information change when a bit is copied from one form of storage to another? For example, does the information change when a bit implemented as a voltage level on a wire is copied to a tiny part of a disk?