All computer data are represented by bits. The data can be numbers, characters, currency amounts, photos, recordings, etc. All are simply a string of bits. Bits are grouped into 8-bit chunks called bytes. For character data, such as the letters in a person's name, one character will fit into one byte. Bytes are used to measure sizes of noncharacter data as well. For example, a given picture can be said to be 100,000 bytes in size. This statement means the length of the bit string that represents the picture is 100,000 bytes or 800,000 bits (because there are 8 bits per byte).
The specifications for the size of main memory, disk, and other computer devices are expressed in bytes. A kilobyte, abbreviated K, is a collection of 1,024 bytes. A megabyte, or MB, is 1,024 kilobytes. A gigabyte, or GB, is 1,024 megabytes; a terabyte or TB, is 1,024 gigabytes; a petabyte, or PB, is 1,024 terabytes; an exabyte, or EB, is 1,024 petabytes; and a zetabyte, or ZB, is 1,024 exabytes.