binary prefix

    (Or "IEC prefix") A prefix used with a unit of data to
   mean multiplication by a power of 1024.  Binary prefixes are most
   often used with "byte" (e.g. "kilobyte") but also with bit
   (e.g. "megabit").

   For example, the term kilobyte has historically been used to
   mean 1024 bytes, and megabyte to mean 1,048,576 bytes.  The
   multipliers 1024 and 1,048,576 are powers of 1024, which is itself
   a power of two (1024 = 2^10).  It is this factor of two that gives
   the name "binary prefix".

   This is in contrast to a decimal prefix denoting a power of
   1000, which is itself a power of ten (1000 = 10^3).  Decimal
   prefixes are used in science and engineering and are specified in
   widely adopted SI standards.  Note that the actual prefix - kilo
   or mega - is the same, it is the interpretation that differs.

   The difference between the two interpretations increases with each
   multiplication, so while 1000 and 1024 differ by only 2.4%, 1000^6
   and 1024^6 differ by 15%.

   The 1024-based interpretation of prefixes is often still used
   informally and especially when discussing the storage capacity of
   random-access memory.  This has lead to storage device
   manufacturers being accused of false marketing for using the
   decimal interpretation where customers might assume the larger,
   historical, binary interpretation.

   In an attempt to clarify the distinction, in 1998 the IEC
   specified that kilobyte, megabyte, etc. should only be used for
   powers of 1000 (following SI).  They specified new prefixes for
   powers of 1024 containing "bi" for "binary": kibibyte,
   mebibyte, etc.; an idea originally propsed by IUPAC.  IEC also
   specified new abbreviations Ki, Mi, etc. for the new prefixes.
   Many other standards bodies such as NIST, IEEE and BIPM
   support this proposal but as of 2013 its use is rare in
   non-technical circles.

   Specific units of IEC 60027-2 A.2 and ISO/IEC 80000

    IEC prefix	   Representations				Customary prefix
    Name  Symbol  Base 2  Base		Base 10		Name	Symbol
   					   1024		(approx)
    kibi  Ki	   2^10	   1024^1	1.02x10^3	kilo	k, K
    mebi  Mi	   2^20	   1024^2	1.05x10^6	mega	M
    gibi  Gi	   2^30	   1024^3	1.07x10^9	giga	G
    tebi  Ti	   2^40	   1024^4	1.10x10^12	tera	T
    pebi  Pi	   2^50	   1024^5	1.13x10^15	peta	P
    exbi  Ei	   2^60	   1024^6	1.15x10^18	exa     E
    zebi  Zi	   2^70	   1024^7	1.18x10^21	zetta	Z
    yobi  Yi	   2^80	   1024^8	1.21x10^24	yotta	Y

   (2013-11-04)