Bit

Here is a table that summarizes the characteristics of the two types of computer memory.

Characteristic	True for Main Memory	True for Secondary Memory
Closely connected to the processor.	X
Holds the programs and data the processor is actively using.	X
Used for long term storage.		X
Interacts with processor millions of times per second.	X
Contents is easily changed.	X	X
Relatively low capacity.	X
Relatively huge capacity.		X
Fast access.	X
Slow access.		X
Connected to main memory.		X
Holds programs and data.	X	X
Organized into files.		X

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.