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:
