Units of information are a way of measuring a quantity of information or an entropy.

Primary units

Comparison of units of information: bit, trit, nat, ban. Quantity of informations is the height of bars. Dark green level is the "Nat" unit.

Small amount of information just as logarithm of number of states. According to Shannon, The choice of a logarithmic base corresponds to the choice of a unit for measuring information.

The minimal integer, whose logarithm is positive, is 2. The unit, corresponding to it is bit. Bit is the base of information measurement in modern information technologies. The unit, corresponding to the number 3 is trit, which is equal to bit. The unit, corresponding to the number 10: ban = bit.

Since the base of natural logarithm is not an integer, such unit as Nat is usually not applied to digital information, but is well known in theory.

Units derived from bit

There have been some attempts to construct unambiguous terms for bit blocks of some sizes.^[1] Terms in italic are strictly jargon, not serve as units (in the proper sense) and not very common.

• 2 bits: crumb, quad, quarter, tayste, tydbit
• 4 bits: nibble, nybble, sometimes "half-byte"
• 5 bits: nickel, nyckle
• 8 bits: byte, octet
• 10 bits: deckle
• 16 bits: plate, playte, chomp, chawmp (on a 32-bit machine)
• 18 bits: chomp, chawmp (on a 36-bit machine)
• 32 bits: dinner, dynner, gawble (on a 32-bit machine)
• 48 bits: gobble, gawble (under circumstances that remain obscure)

The following therms allows precise meaning on bits quantities:

• 1 bit is binary digit
• 8 bits: byte or octet, 1B(yte) = 8b(its)
• 16 bits: doublet
• 32 bits: quadlet
• 64 bits: octlet

Byte

Main article: Octet (computing)

Large amounts of information are almost always counted in bytes rather than bits, and it is generally used as an atomic unit when addressing memory. See below a clarification of the term byte.

Kilobyte

Whether used to denote 1024 bytes (a kibibyte, or KiB), or more correctly, 1000 bytes (kB), this is a convenient order of magnitude to express:

• the typical sector of a hard disk: 512 bytes = ½ KiB
• the classical block size in UNIX filesystems: 1024 bytes = 1 KiB
• a CD-ROM sector: 2048 bytes = 2 KiB
• a memory page in x86 (since Intel 80386): 4096 bytes = 4 KiB

Megabyte

Units megabyte MB = 1000000 bytes and mebibyte MiB = 1024 KiB = 1048576 bytes.

Electronic memory is commonly measured in mebibytes, but hard disks are (or were) measured mainly in megabytes.

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. (June 2008)

Gigabyte

Units gigabyte GB = 10⁹ bytes and gibibyte GiB = 1024 MiB = 2³⁰ bytes.

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. (June 2008)

Terminology

What is "byte"?

Main article: Byte

The word "byte" has two closely related meanings:

1. A contiguous sequence of a fixed number of bits (binary digits).
2. A contiguous sequence of bits within a binary computer that comprises the smallest addressable sub-field of the computer's natural word-size.

In modern computing, the use of a byte to mean 8 bits has become nearly ubiquitous in both senses. The term octet is used in very strict speech (such as RFCs) to avoid any ambiguity.

SI vs. Binary prefixes

Main article: Binary prefix

The prefixes historically used for byte measurements are usually the same as the SI prefixes used for other measurements, but have slightly different values. The former are based on powers of 1,024 (2¹⁰), a convenient binary number, while the SI prefixes are based on powers of 1,000 (10³), a convenient decimal number. The table below illustrates these differences.

Sometimes "K" is used instead of "k". The use of "K" as a prefix has no meanings for the SI.

In 1998, the IEC, then the IEEE, published a new standard describing binary prefixes:

References

• Representation of numerical values and SI units in character strings for information interchanges