Binary is an alternative number system which works very good for computers. Humans have ten fingers; that's probably why we use ten digits (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) in our number system (decimal), but it is simple for a computer to use only two digits (0 and 1). Ones and zeros can be shown with high or low voltage, closed or open switches, aligned or misaligned magnetic particles, etc. A byte is a group of eight bits, and it is the standard unit by which data is stored. There are 256 dissimilar combinations of zeros and ones you can make with one byte, from 00000000 to 11111111. This is sufficient to cover all the ASCII characters. If more than 256 values are required, then more than one byte can be used. With two bytes, there are 65536 possible combinations of ones and zeros. These bytes can show any kind of data. For example, a picture may be made up of thousands of pairs of bytes, with each pair of bytes signifying a single dot in one of 65536 colors. Put together all these dots (known as pixels) and you have a full-color picture (most picture data is also compressed).