Kibibyte

The unit prefix kibi specifies multiplication by 2¹⁰ (1024). It was derived as a portmanteau from 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), all IEC binary prefixes start with an uppercase letter.[5]

Therefore, the definition of the kibibyte is:

1 kibibyte (KiB) = 2¹⁰ bytes = 1024 bytes.

The next larger unit of information in the sequence with IEC binary prefixes is the mebibyte (MiB) (2²⁰ bytes):

1024 kibibytes = 1 mebibyte.

IEC specification 80000-13 defines one byte as 8 bits (1 B = 8 bit). Therefore,

1 kibibyte = 8192 bits.

The kibibyte is closely related to the kilobyte, which equals 1000 bytes, as the prefix kilo is defined in the International System of Units.

Within the field of computer science, during the 1970s and 1980s, the term kilobyte generally meant 1024 bytes, but was sometimes used to mean 1000 bytes. When describing random access memory, kilobyte typically meant 1024 bytes, but when describing disk drive storage, kilobyte typically meant 1000 bytes.[6] The errors associated with this ambiguity are relatively small with the lower prefixes in the series, i.e. for kilo and mega, but grows to substantial differences beyond.

In 1995, to resolve this ambiguity, the International Union of Pure and Applied Chemistry's Interdivisional Committee on Nomenclature and Symbols proposed new prefixes kibi, mebi, etc for powers of 1024.[7][8] The kibi proposal was formally adopted by the International Electrotechnical Commission in December 1998, and published in January 1999.[9][10]

In 1999, Donald Knuth proposed to call the kibi unit a large kilobyte (KKB), but his proposal was not adopted.[11]

In spite of the formal adoption of the term kibibyte in 1999, the term "kilobyte" continues to be used to mean 1024 bytes in some product advertising and other non-scientific contexts.[12][13][14]

• IEEE 1541
• Timeline of binary prefixes