What is a Bit?

A bit is a discrete "piece" of information. It is a physical entity.

Consider a coin. It has two information states Heads or Tails. So a sequence of bits can represent a series of successive coin tosses.

A mechanism, like a box that flips coins, which produces a series of bits, is sometimes called an information source. Even if this information source produces "noise" (e.g. random bits of information) it is still generating physical information.

Consider a coin that is flipped twice: What are the possible outcomes?

1. HH
2. HT
3. TH
4. TT

Four equally likely outcomes can be represented by two bits of individual information (e.g. H or T).

For three coin flips there are 8 different equally likely outcomes and three bits of information is needed to represent those 8 possible outcomes.

So if something has N equally likely outcomes, it will take

b = log₂ N

bits to represent this.

Powers of 2 table:

Now let's go back to the case of 3 bits that represent 8 equally likely outcomes.

The next step is to have "protocol" mapping onto the bits. That is, column A makes sense as a protocol while column B does not. This is precisely what the ASCII standard is. To represent a character (in the english language) by a unique pattern of bits. In fact, it is a unique pattern of 8 bits and 8 bits make up a BYTE .

Each character then requires 1 BYTE of memory to be stored.

An arithmatic example:

A useful binary to decimal calculator