[USMA:17252] Binary Prefixes

[kilopascal]

2002-01-06   Dear Mr. Ross,     In reading down your web page: http://www.friesian.com/quanta.htm#note-3, I came across the following:   Consistency, however, is not always possible. Although the beauty of the metric system is its foundation on decimal values, which has sold it to every country in the world except the United States, and some other oddballs -- though even American customary units are officially defined in metric terms -- some customary units and strange usages have been retained or crept in for convenience. Most importantly, the systematization of decimal counting failed to anticipate the binary basis of modern computer technology. The powers of 2 now rival the powers of 10, and even metric prefixes have been corrupted. Thus, when the unit "kilobyte" ("kB" or just "K") is used, it does not really mean 1000 bytes of information. It means 1024 bytes, i.e. 210. A "megabyte" ("MB" or "Meg") is not 1,000,000 bytes, but 1,048,576 bytes, i.e. 1024 x 1024 or 220.   The information stated above is no longer correct.  In fact it has never been.  The SI prefixes have always had a decimal meaning and never a binary meaning that was officially or legally sanctioned.  The BIPM and CGPM do not recognise alternate meanings to the SI prefixes.  If it is done, it is done without the authority of the standards bodies.  In not all cases in computer technology have the SI prefixes been corrupted to mean powers of 2.  In the case of hard drives, the prefixes retain their SI meaning.  Thus a 10 GB hard drive contains 10 x 10^9 B and not 10 x 2^30 B.  The abuse of the prefixes in computer technology is inconsistent. To address the need for powers of 2 prefixes, the IEC in 1998 authorised a new set of prefixes to handle the powers of 2.  These prefixes are similar to the SI prefixes, but are meant to be used when expressing capacity in powers of 2.  The binary prefixes use the SI prefixes, kilo, mega, giga, tera, etc and contract them with the word "binary" to come up with Kibi, Mibi, Gibi, Tibi, etc.  These prefixes are only to be combined with the units bit and byte (B).  Thus a Kibibyte is 2^10 B, a Mibibyte is 2^20 B, a Gibibyte is 2^30 B, etc.  The symbols are Ki, MI, Gi, etc.   For more information on these prefixes, visit the site:  http://physics.nist.gov/cuu/Units/binary.html   Also note that the unit Angstrom is not a proper SI unit and is deprecated.  It is obsolete and is fast disappearing.  In fact, I never hear or see it anymore, except in something old.  The proper replacement is the nanometre equal to 10^-9 m.   Please review the information and update your webpage accordingly.   Best Regards,   John