Binary prefix

A binary prefix is a prefix to indicate a multiple of a unit of measurement by an integer power of two. The most commonly used binary prefixes are kibi (symbol Ki, meaning 210= 1024), mebi (Mi, 220 = 1048576), and gibi (Gi, 230 = 1073741824). They are most often used in information technology as multipliers of bit and byte, when expressing the capacity of storage devices or the size of computer . The binary prefixes "kibi", "mebi", etc. were defined in 1999 by the International Electrotechnical Commission (IEC), in the IEC 60027-2 standard (Amendment 2). They were meant to replace the metric (SI) decimal power prefixes, such as "kilo" ("k", 103 = 1000), "mega" ("M", 106 = 1000000) and "giga" ("G", 109 = 1000000000), that were commonly used in the computer industry to indicate the nearest powers of two. For example, a memory module whose capacity was specified by the manufacturer as "2 megabytes" or "2 MB" would probably hold 2 × 220 = 2097152 bytes, instead of 2 × 106 = 2000000. On the other hand, hard disk whose capacity was specified by the manufacturer as "10 gigabytes" or "10 GB" would probably hold 10 × 109 = 10000000000 bytes, or a little more than that, but less than 10 × 230 = 10737418240; and a file whose size was listed as "2.3 GB" may have a size closer to 2.3 × 230 ≈ 2470000000 or to 2.3 × 109 = 2300000000, depending on the program or operating system providing that measurement. This ambiguity was often confusing to computer system users and even resulted in lawsuits. The IEC 60027-2 binary prefixes were later incorporated in the ISO/IEC 80000 standard and supported by other major standards bodies, including the BIPM (which defines the SI system), the US NIST, and the European Union. Prior to the 1999 IEC standard, some industry organizations, such as the Joint Electron Device Engineering Council (JEDEC), attempted to redefine the terms kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB, and GB in the binary sense, for use in storage capacity masurements.