IEC 60027 (formerly IEC 27) is a technical international standard for letter symbols published by the International Electrotechnical Commission (IEC), comprising the following parts: A closely related international standard on quantities and units is ISO 31.
The revised harmonized standard is known as ISO/IEC 80000, Quantities and units.
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 added prefixes zebi- (Zi) and yobi- (Yi).
The only significant change is the addition of explicit definitions for some quantities.