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Prefixes are morphemes (specific groups of letters with particular semantic meaning) that are added onto the beginning of roots and base words to change their meaning. Prefixes are one of the two predominant kinds of affixes—the other kind is suffixes, which come at the end of a root word.
Unlike suffixes, which can be either inflectional (changing only the grammatical function of a word without changing its basic meaning) or derivational (creating a word with an entirely new meaning), prefixes can only be derivational; adding a prefix always changes the basic meaning of the word.
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The standard metric prefixes used in the Syst?me International d'Units (SI) conventions for scientific measurement.

Here are the SI magnifying prefixes, along with the corresponding binary interpretations in common use:

prefix abr decimal binary

yocto- 1000^-8 zepto- 1000^-7 atto- 1000^-6 femto- f 1000^-5 pico- p 1000^-4 nano- n 1000^-3 micro- * 1000^-2 * Abbreviation: Greek mu milli- m 1000^-1

kilo- k 1000^1 1024^1 = 2^10 = 1,024 mega- M 1000^2 1024^2 = 2^20 = 1,048,576 giga- G 1000^3 1024^3 = 2^30 = 1,073,741,824 tera- T 1000^4 1024^4 = 2^40 = 1,099,511,627,776 peta- 1000^5 1024^5 = 2^50 = 1,125,899,906,842,624 exa- 1000^6 1024^6 = 2^60 = 1,152,921,504,606,846,976 zetta- 1000^7 1024^7 = 2^70 = 1,180,591,620,717,411,303,424 yotta- 1000^8 1024^8 = 2^80 = 1,208,925,819,614,629,174,706,176

"Femto" and "atto" derive not from Greek but from Danish.

The abbreviated forms of these prefixes are common in electronics and physics.

When used with bytes of storage, these prefixes usually denote multiplication by powers of 1024 = 2^10 (K, M, and G are common in computing). Thus "MB" stands for megabytes (2^20 bytes). This common practice goes against the edicts of the BIPM who deprecate the use of these prefixes for powers of two. The formal SI prefix for 1000 is lower case "k"; some, including this dictionary, use this strictly, reserving upper case "K" for multiplication by 1024 (KB is thus "kilobytes").

Also, in data transfer rates the prefixes stand for powers of ten so, for example, 28.8 kb/s means 28,800 bits per second.

The unit is often dropped so one may talk of "a 40K salary" (40000 dollars) or "2 meg of disk space" (2*2^20 bytes).

The accepted pronunciation of the initial G of "giga-" is hard, /gi'ga/.

Confusing 1000 and 1024 (or other powers of 2 and 10 close in magnitude) - for example, describing a memory in units of 500K or 524K instead of 512K - is a sure sign of the marketroid. For example, 3.5" microfloppies are often described as storing "1.44 MB". In fact, this is completely specious. The correct size is 1440 KB = 1440 * 1024 = 1474560 bytes. Alas, this point is probably lost on the world forever.

In 1993, hacker Morgan Burke proposed, to general approval on Usenet, the following additional prefixes: groucho (10^-30), harpo (10^-27), harpi (10^27), grouchi (10^30). This would leave the prefixes zeppo-, gummo-, and chico- available for future expansion. Sadly, there is little immediate prospect that Mr. Burke's eminently sensible proposal will be ratified.


Related to the prefix notation.
This article is provided by FOLDOC - Free Online Dictionary of Computing (
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



an affix, part of a word that comes before the root and changes its lexical or grammatical meaning, for example, its aspect.

In the Indo-European languages, the relation between prefixes and adverbs and certain prepositions can be traced historically. Prefixes can enter into the composition of nearly all autoseman-tic words except numerals and pronouns. Several prefixes may occur in a word, such as the Russian po-na-s-bival. In some Indo-European languages there are prefixes that, when stressed in certain verbal forms, become separated from the verb and are placed after it—for example, German weggehen, “to go away,” and geheweg, “go away”; but beschreiben, “to describe,” and beschreibe, “describe.” In some languages, such as Swahili, the prefix is the principal type of affix. In the Caucasian and Semitic languages, verb conjugation is totally or primarily of the prefixal type.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The beginning or to add to the beginning. To prefix a header onto a packet means to place the header characters in front of the packet. "To prefix" at the beginning is the opposite of "to append" characters at the end. See prepend.
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