A Change in Terminology

A new standard for measurements of data was proposed in 1995 by the International Organization for Standardization, and approved and in use according to The NIST Reference (see http://physics.nist.gov/cuu/Units/binary.html It clears up the problem of there being now THREE different values used for a "Megabyte" in particular, and the similar confusion with Kilobyte, Gigabyte, etc. It does this by creating a new "binary" set of measurements so "Giga-Binary-byte (Gibibyte or GI byte) will be defined as different than "Gigabyte".

Value of "Megabyte"	Exponential Equivalent	Definition now used by	Proposed usage
1, 048, 576	2²⁰	Computer scientists in general; used in computer programs and as a measure of memory, program size, etc.	The new MEBIBYTE (aka MI byte short for Mega-Binary-Byte). Reflects power of two (binary) value as typically used data processing. You might want to see Don Knuth's suggestion of calling this value LARGE MEGABYE aka MMB.
1, 000, 000	10⁶	Mostly makers of hard disks, and in a few cases other components, such as some types of network hardware;	Officially defined as the MEGABYTE. Reflects power of ten (decimal) value as typically used in metric system.
1, 024, 000	2¹⁰ x 1,000 (presumably) 2^19.96578...	Value as used for floppy disks. A 1.44MB floppy has a capacity of exactly 1,474,560 bytes instead of 1,509,949.44 bytes (rounding error) or 1,440,000 bytes when either of the two above are used.	Remains as an artifact of marketing types trying to dumb-down the general population to their own sub par mental capacities. May I suggest MORONABYTE?

As of this writing (22-Mar-1999) I unfortunately have not yet seen the proposed standard, but I am under the impression that it contains just the prefixes Ki (Kibibyte), Mi (Mebibyte), Gi (Gibibyte), and Ti (Tibibyte).

I've extrapolated in my table of Powers of Two that the proposal does or will include the prefixes Pi (Pebibyte), Ei (Exbibyte), Zi (Zebibyte), and Yi (Yobibyte).

When and if the standard changes I will update this table to show the differences between, for instance, a "Kilobyte" and a "Kibibyte".

References:

Copyright © 1999 Kevin J. Walsh	[back to Powers of Two]
walsh@njit.edu /KJW	_disclaimer