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3.4. Bits

Bits

Each hole (or spot where there is no hole punched) in this card represents a bit of information.

A bit (short for “BInary digiT”) is a single on/off value. Only these two values are possible, though 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. Here are some ways that bits are implemented:

• A mechanical electrical switch (like a light switch.)

• Voltage on a wire.

• A light bulb being on or off.

• The state of a single transistor.

• The magnetic charge on a tiny part of the surface of a disk.

• The presence or absence of a hole punched in a card.

• A tiny part of the light-reflecting surface of a CD.

• Part of a radio signal.

Computers do all of their processing in terms of bits - any piece of information a computer stores or manipulates is stored as a sequence of these on/off values. For different purposes, a computer may use any of the mechanisms listed above (or many others) to represent those bits.

Self Check

What is a bit?

• A single on/off value.
• A value of "one."
• A large section of computer memory.
• Enough memory to store a character.

Which one of the following statements is FALSE?

• The method used to implement a bit does not affect the information it represents
• A light bulb that is "Off" represents the same thing as an "Off" represented by a hole that is not punched
• A bit may be implemented as a small part of a magnetic disk.
• This is how hard drives store information
• Copying a bit from one medium to another does not affect the information it represents.
• Computers do this all the time - turn an electrical signal in a circuit into a magnetic field on a disk. Or turn a hole into a punch card into an electrical signal
• A bit is always implemented as something electrical.

Materials on this page adapted with permission from from:
Introduction to Computer Science using Java by Bradley Kjell (CC BY-NC 3.0)

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