The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024, therefore 1 kibibyte is 1024bytes. The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission (IEC) in 1999 and has been accepted for use by all major standards organizations. It was designed to replace the kilobyte used in some computer science contexts to mean 1024 bytes, which conflicts with the SI definition of the prefix kilo.
The prefix kibi is derived as a portmanteau of the words kilo and binary, indicating its origin in the closeness in value to the SI prefix kilo (1000). While the SI prefix is written with lowercase (k), the IEC prefix starts with an uppercase letter.
The kibibyte is closely related to the kilobyte. The latter may be used in some contexts as a synonym for the kibibyte, but formally refers to 103 bytes = 1000 bytes, as the prefix is defined in the International System of Units.
The binary interpretation of the metric prefixes causes relatively small differences with the smallest prefixes in the series, i.e. for kilo and mega, but grows to substantial differences beyond (see Deviation between powers of 1024 and powers of 1000).
In Introduction to MMIX, Donald Knuth proposed that this unit be called a large kilobyte (abbreviated KKB). Other early proposals included using the Greek lowercase letter κ (kappa) for 1024 bytes (and using k exclusively for 1000), bK, KB, and others. See Binary prefix#Early suggestions.
Adoption of the binary prefixes has been limited, primarily being used in open source software. In most cases the kilobyte continues to be used to refer to a power of ten as well as a power of two.
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