# What is Binary Number

By Xah Lee. Last updated: . Last updated: .

### What is Binary Digit

Binary digit system is a notation to repsent numbers.

In decimal system, we use 10 symbols, 0 to 9. When a number is larger than 9, we start over by placing a new digit on the left. For example, 10 is 1 on left and 0 on right.

A binary number notation uses just 2 symbols.

A binary digit is either 1 or 0. For example, `1001` is four binary digits.

A binary digit is also called bit. So, `1001` is 4 bits.

Here's a table showing decimal and binary:

decimalbinary
00
11
210
311
4100

Binary digits is used in computers, because electronics deal with on/off signals, most easily represented by binary digits.

### Possible Size in Binary Number

If a binary number has n digits, it has 2^n possible values.

number of bitspossible distinct values
12
24
38
416
532
664
7128
8256

### What is Bit

A bit is a single binary digit. It's has 2 possible values, usually represented as 1 or 0. With 1 usually means on, 0 is off. Or, 1 is true, 0 is false.