Units of information

The byte, 8 bits, 2 nibbles, is possibly the most commonly known and used base unit to describe data size.

In 1928, Ralph Hartley observed a fundamental storage principle,[2] which was further formalized by Claude Shannon in 1945: the information that can be stored in a system is proportional to the logarithm of N possible states of that system, denoted logb N. Changing the base of the logarithm from b to a different number c has the effect of multiplying the value of the logarithm by a fixed constant, namely logc N = (logc b) logb N. Therefore, the choice of the base b determines the unit used to measure information.

In particular, if b is a positive integer, then the unit is the amount of information that can be stored in a system with b possible states.

The IEEE 1541-2002 standard specifies "B" (upper case) as the symbol for byte (IEC 80000-13 uses "o" for octet in French, but also allows "B" in English).

Bytes, or multiples thereof, are almost always used to specify the sizes of computer files and the capacity of storage units.

A group of four bits, or half a byte, is sometimes called a nibble, nybble or nyble.

[7] Computers usually manipulate bits in groups of a fixed size, conventionally called words.

Virtual memory systems partition the computer's main storage into even larger units, traditionally called pages.

[9] The JEDEC memory standard JESD88F notes that the definitions of kilo (K), giga (G), and mega (M) based on powers of two are included only to reflect common usage, but are otherwise deprecated.