**IEC 60027** (formerly **IEC 27**) is a technical international standard for letter symbols published by the International Electrotechnical Commission, comprising the following parts:

- IEC 60027-1: General
- IEC 60027-2: Telecommunications and electronics
- IEC 60027-3: Logarithmic and related quantities, and their units
- IEC 60027-4: Symbols for quantities to be used for rotating electrical machines
- IEC 60027-6: Control technology
- IEC 60027-7: Physiological quantities and units

A closely related international standard on quantities and units is ISO 31. The ISO 31 and IEC 60027 Standards are being revised by the two standardization organizations in collaboration. The revised harmonized standard is known as ISO/IEC 80000, Quantities and units. It supersedes both ISO 31 and part of IEC 60027.

IEC 60027-2 Amendment 2, as published in January 1999, was the first international standard defining the binary prefixes, as proposed by International Electrotechnical Commission (IEC) since 1996 (*kibi-* (Ki), *mebi-* (Mi), *gibi-* (Gi) and *tebi-* (Ti))^{[1]} but extended them up to *pebi* (Pi) and *exbi-* (Ei).^{[2]}^{[3]} This didn't change in the second edition of the standard, published in 2000,^{[4]}^{[5]} but the third edition in 2005 finally added prefixes *zebi-* (Zi) and *yobi-* (Yi).^{[6]} The harmonized ISO/IEC IEC 80000-13:2008 standard supersedes subclauses 3.8 and 3.9 of IEC 60027-2:2005. The only significant change is the addition of explicit definitions for some quantities.^{[7]}

**^**"1996 IUCr IUPAC Interdivisional Committee on Nomenclature and Symbols (IDCNS) report". Chester.iucr.org. Archived from the original on 2013-06-13. Retrieved 2012-01-26.**^**"These prefixes for binary multiples, which were developed by IEC Technical Committee (TC) 25, Quantities and units, and their letter symbols, with the strong support of the International Committee for Weights and Measures (CIPM) and the IEEE, were adopted by the IEC as Amendment 2 to IEC International Standard IEC 60027-2: Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics."**^**"IUCR 1999 report on IUPAC Interdivisional Committee on Nomenclature and Symbols". Journals.iucr.org. Retrieved 2012-01-26.**^**IEC 60027-2 (2000-11) Ed. 2.0**^**Thor, A. J. (2000). "Prefixes for binary multiples" (PDF).*Metrologia*.**37**(81): 81. Bibcode:2000Metro..37...81T. doi:10.1088/0026-1394/37/1/12.**^**"HERE COME ZEBI AND YOBI" (Press release). International Electrotechnical Commission. 2005-08-15. Archived from the original on September 12, 2009.**^**"niso, New Specs and Standards". Niso.org. Archived from the original on 2008-12-08. Retrieved 2012-01-26.

- "IEC 60027-7 (2010-05) Ed. 1.0" (IEC Catalog, www.iec.ch)
- "IEC 60027-2 (2005-08) Ed. 3.0 Bilingual" (preview)
- "IEC 60027-1", "IEC 60027-2", "IEC 60027-3", "IEC 60027-4", "IEC 60027-5", "IEC 60027-6", "IEC 60027-7" at International Electrotechnical Commission

A binary prefix is a unit prefix for multiples of units in data processing, data transmission, and digital information, notably the bit and the byte, to indicate multiplication by a power of 2.

The computer industry has historically used the units kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB, and GB, in at least two slightly different measurement systems. In citations of main memory (RAM) capacity, gigabyte customarily means 1073741824 bytes. As this is a power of 1024, and 1024 is a power of two (210), this usage is referred to as a binary measurement.

In most other contexts, the industry uses the multipliers kilo, mega, giga, etc., in a manner consistent with their meaning in the International System of Units (SI), namely as powers of 1000. For example, a 500 gigabyte hard disk holds 500000000000 bytes, and a 1 Gbit/s (gigabit per second) Ethernet connection transfers data at 1000000000 bit/s. In contrast with the binary prefix usage, this use is described as a decimal prefix, as 1000 is a power of 10 (103).

The use of the same unit prefixes with two different meanings has caused confusion. Starting around 1998, the International Electrotechnical Commission (IEC) and several other standards and trade organizations addressed the ambiguity by publishing standards and recommendations for a set of binary prefixes that refer exclusively to powers of 1024. Accordingly, the US National Institute of Standards and Technology (NIST) requires that SI prefixes only be used in the decimal sense: kilobyte and megabyte denote one thousand bytes and one million bytes respectively (consistent with SI), while new terms such as kibibyte, mebibyte and gibibyte, having the symbols KiB, MiB, and GiB, denote 1024 bytes, 1048576 bytes, and 1073741824 bytes, respectively. In 2008, the IEC prefixes were incorporated into the international standard system of units used alongside the International System of Quantities (see ISO/IEC 80000).

Cmp (Unix)In computing, cmp is a command-line utility for computer systems that use Unix or a Unix-like operating system. It compares two files of any type and writes the results to the standard output. By default, cmp is silent if the files are the same; if they differ, the byte and line number at which the first difference occurred is reported. The command is also available in the OS-9 shell.

ExbibitThe exbibit is a multiple of the bit, a unit of digital information storage, prefixed by the standards-based multiplier exbi (symbol Ei), a binary prefix meaning 260. The unit symbol of the exbibit is Eibit.

1 exbibit = 260 bits = 1152921504606846976bits = 1024 pebibitsThe exbibit is closely related to the exabit, the corresponding unit using the metric prefix exa, which is 1018 bits = 1000000000000000000bits.

GibibitThe gibibit is a multiple of the bit, a unit of information, prefixed by the standards-based multiplier gibi (symbol Gi), a binary prefix meaning 230. The unit symbol of the gibibit is Gibit.

1 gibibit = 230 bits = 1073741824bits = 1,024 mebibitsThe gibibit is closely related to the gigabit, the corresponding unit using the metric prefix giga, which is 109 bits.

Giga-Giga ( or ) is a unit prefix in the metric system denoting a factor of a (short-form) billion (109 or 1000000000). It has the symbol G.

Giga is derived from the Greek word γίγας, meaning "giant". The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 109×".When referring to information units in computing, such as gigabyte, giga may sometimes mean 1073741824 (230), although such use is inconsistent, contrary to standards and has been discouraged by the standards organizations. The inconsistency is that gigabit is never (or very rarely) used with the binary interpretation of the prefix, while gigabyte is sometimes used this way. The binary prefix gibi has been adopted for 230, while reserving giga exclusively for the metric definition.

IEC-P27-1IEC-P27-1 (or ISO IR-143) is an 8-bit character set developed by the IEC. When combined with the ISO/IEC 646 character set, this includes all characters required to print the symbols defined in IEC 60027-1.

IEEE 1541-2002IEEE 1541-2002 is a standard issued in 2002 by the Institute of Electrical and Electronics Engineers (IEEE) concerning the use of prefixes for binary multiples of units of measurement related to digital electronics and computing.

While the International System of Units (SI) defines multiples based on powers of ten (like k = 103, M = 106, etc.), a different definition is sometimes used in computing, based on powers of two (like k = 210, M = 220, etc.) This is due to the use of binary addressing for computer memory locations.

In the early years of computing, there was no significant error in using the same prefix for either quantity (210 = 1024 and 103 = 1000 are equal, to two significant figures). Thus, the SI prefixes were borrowed to indicate nearby binary multiples for these computer-related quantities.

Meanwhile, manufacturers of storage devices, such as hard disks, traditionally used the standard decimal meanings of the prefixes, and decimal multiples are used for transmission rates and processor clock speeds as well. As technology improved, all of these measurements and capacities increased. As the binary meaning was extended to higher prefixes, the absolute error between the two meanings increased. This has even resulted in litigation against hard drive manufacturers, because some operating systems report the size using the larger binary interpretation.

Moreover, there is not a consistent use of the symbols to indicate quantities of bits and bytes – the unit symbol "Mb", for instance, has been widely used for both megabytes and megabits. IEEE 1541 sets new recommendations to represent these quantities and unit symbols unambiguously.

After a trial period of two years, in 2005, IEEE 1541-2002 was elevated to a full-use standard by the IEEE Standards Association, and was reaffirmed on 27 March 2008.

IEEE 1541 is closely related to Amendment 2 to IEC International Standard IEC 60027-2. The IEC standard was harmonized into the common ISO/IEC IEC 80000-13:2008 – Quantities and units – Part 13: Information science and technology. This standard uses 'bit' as the symbol for bit, as opposed to 'b'.

ISO/IEC 80000ISO 80000 or IEC 80000 is an international standard promulgated jointly by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC).

The standard introduces the International System of Quantities (ISQ). It is a style guide for the use of physical quantities and units of measurement, formulas involving them, and their corresponding units, in scientific and educational documents for worldwide use. In most countries, the notations used in mathematics and science textbooks at schools and universities follow closely the guidelines in this standard.The ISO/IEC 80000 family of standards was completed with the publication of Part 1 in November 2009.

ISO 31ISO 31 (Quantities and units, International Organization for Standardization, 1992) is a deprecated international standard for the use of physical quantities and units of measurement, and formulas involving them, in scientific and educational documents. It is superseded by ISO/IEC 80000.

JEDEC memory standardsThe JEDEC memory standards are the specifications for semiconductor memory circuits and similar storage devices promulgated by the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association, a semiconductor trade and engineering standardization organization.

JEDEC Standard 100B.01 specifies common terms, units, and other definitions in use in the semiconductor industry. JESC21-C specifies semiconductor memories from the 256 bit static RAM to the latest DDR3 SDRAM modules. In August 2011, JEDEC announced that its DDR4 standard was expected to be published in mid-2012.

KibibitThe kibibit is a multiple of the bit, a unit of digital information storage, using the standard binary prefix kibi, which has the symbol Ki, meaning 210. The unit symbol of the kibibit is Kibit.

1 kibibit = 210 bits = 1,024 bitsThe kibibit has existed since 1998 and is closely related to the kilobit, which is equal to 103 bits = 1,000 bits. However, a kibibit is 1024 bits. Likewise, a kibibyte is 1,024 bytes.

The binary prefixes form part of the International System of Quantities (ISQ).

KibibyteThe kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 210, or 1024; therefore, 1 kibibyte is 1024 bytes. The unit symbol for the kibibyte is KiB.The unit was established by the International Electrotechnical Commission (IEC) in 1998, has been accepted for use by all major standards organizations, and is part of the International System of Quantities. The kibibyte was designed to replace the kilobyte in those computer science contexts in which the term kilobyte is used to mean 1024 bytes. The interpretation of kilobyte to denote 1024 bytes, conflicting with the SI definition of the prefix kilo (1000), used to be common.

MebibitThe mebibit is a multiple of the bit, a unit of information, prefixed by the standards-based multiplier "mebi" (symbol Mi), a binary prefix meaning 220. The unit symbol of the mebibit is Mibit.

1 mebibit = 220 bits = 1048576bits = 1024 kibibitsThis unit is most useful for measuring RAM and ROM chip capacity.

The mebibit is closely related to the megabit which equals 106 bits = 1,000,000 bits.

Throughout the 1980s and 1990s, video game manufacturers sometimes reported the amount of internal cartridge read-only memory (ROM) on packaging in megabits, where 1 megabit equaled 128 kibibyte and 8 megabits were 1 mebibyte of ROM, containing game instructions and data.

MebibyteThe mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220; therefore one mebibyte is equal to 1048576bytes = 1024 kibibytes. The unit symbol for the mebibyte is MiB.

The unit was established by the International Electrotechnical Commission (IEC) in 1998. It was designed to replace the megabyte when used in the binary sense to mean 220 bytes, which conflicts with the definition of the prefix mega in the International System of Units (SI) as a multiplier of 106.

The binary prefixes have been accepted by all major standards organizations and are part of the International System of Quantities. Many Linux distributions use the unit, but it is not widely acknowledged within the industry or media.

PebibitThe pebibit is a multiple of the bit, a unit of digital information storage, prefixed by the standards-based multiplier pebi (symbol Pi), a binary prefix meaning 250. The unit symbol of the pebibit is Pibit.

1 pebibit = 250 bits = 1125899906842624bits = 1024 tebibitsThe pebibit is closely related to the petabit, the corresponding unit using the metric prefix peta, which is 1015 bits.

Sound exposureSound exposure is the integral, over time, of squared sound pressure. The SI unit of sound exposure is the pascal squared second (Pa2·s).

TebibitThe tebibit is a multiple of the bit, a unit of information, prefixed by the standards-based multiplier tebi (symbol Ti), a binary prefix meaning 240. The unit symbol of the tebibit is Tibit.

1 tebibit = 240 bits = 1099511627776bits = 1024 gibibitsThe tebibit is closely related to the terabit, the corresponding unit using the metric prefix tera, which is 1012 bits.

YobibitThe yobibit is a multiple of the bit, a unit of digital information storage, prefixed by the standards-based multiplier yobi (symbol Yi), a binary prefix meaning 280. The unit symbol of the yobibit is Yibit.1 yobibit = 280 bits = 1208925819614629174706176bits = 1024 zebibitsThe prefixes zebi and yobi were originally not part of the system of binary prefixes, but were added by the International Electrotechnical Commission in August 2006.

ZebibitThe zebibit is a multiple of the bit, a unit of digital information storage, prefixed by the standards-based multiplier zebi (symbol Zi), a binary prefix meaning 270. The unit symbol of the zebibit is Zibit.

1 zebibit = 270 bits = 1180591620717411303424bits = 1024 exbibitsThe prefix zebi was originally not a part of the system of binary prefixes, but was added together with the prefix yobi by the International Electrotechnical Commission in August 2005.

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