Declet (computing)

1000 103 kbit kilobit 10002 106 Mbit megabit 10003 109 Gbit gigabit 10004 1012 Tbit terabit 10005 1015 Pbit petabit 10006 1018 Ebit exabit 10007 1021 Zbit zettabit 10008 1024 Ybit yottabit	1024 210 Kibit kibibit Kbit kilobit 10242 220 Mibit mebibit Mbit megabit 10243 230 Gibit gibibit Gbit gigabit 10244 240 Tibit tebibit - 10245 250 Pibit pebibit - 10246 260 Eibit exbibit - 10247 270 Zibit zebibit - 10248 280 Yibit yobibit -

In computing and telecommunications, a unit of information is the capacity of some standard data storage system or communication channel, used to measure the capacities of other systems and channels. In information theory, units of information are also used to measure the entropy of random variables and information contained in messages.

The most commonly used units of data storage capacity are the bit, the capacity of a system that has only two states, and the byte (or octet), which is equivalent to eight bits. Multiples of these units can be formed from these with the SI prefixes (power-of-ten prefixes) or the newer IEC binary prefixes (power-of-two prefixes). In dimensional analysis, information is considered to be a dimensionless quantity.

In 1928, Ralph Hartley observed a fundamental storage principle, 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 log_bN. 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 log_cN = (log_cb) log_bN. 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 N possible states.

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