As mentioned earlier, computers store all data as patterns of 0s and 1s. Information systems using 0s and 1s are collectively known as binary information systems.

Each 0 or 1 in a binary value is called a bit, which is short for binary digit. This can sometimes be misleading, since not all bits actually represent digits in a number. A bit could be part of any type of information, including numbers, letters of the alphabet, hieroglyphics, Boolean (true/false) values, Chinese characters, encrypted passwords, etc.

A collection of 8 bits is called a byte. A byte is the most common unit of storage for electronic memory, i.e. each memory location holds one byte of data in most computers. It is also usually the smallest amount of data that a machine instruction can process, although it is possible to manipulate individual bits within a byte. Processing data smaller than a byte is generally not as easy as processing whole bytes.

A collection of 4 bits is called a nybble.

A word is the maximum amount of data a CPU can process at once, and is usually 1, 2, 4, or 8 bytes (8 to 64 bits).

Table 15.1, “Basic Binary Units” summarizes the simple binary data quantities.

Numeric data in computers are stored using several different binary number formats, all of which use a finite number of binary digits (bits), and therefore are subject to overflow and round-off or truncation.