noun Computers.
2 20 (1,048,576) bytes.
(loosely) one million bytes. Abbreviation: MB

1965–70; mega- + byte Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
megabyte (ˈmɛɡəˌbaɪt)
computing See also mega- MB, Abbreviation: mbyte 220 or 1 048 576 bytes

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1973, from mega- + byte.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
megabyte   (měg'ə-bīt')  Pronunciation Key 
  1. A unit of computer memory or data storage capacity equal to 1,048,576 bytes (1,024 kilobytes or 220 bytes).

  2. One million bytes.

Our Living Language  : In computer science and industry usage, the prefix mega- often does not have its standard scientific meaning of 1,000,000, but refers instead to the power of two closest to 1,000,000, which is 220, or 1,048,576. The calculation of data storage capacity (measured in bytes) is based on powers of two because of the binary nature of bits (1 byte is 8, or 23, bits). Thus, a megabyte is 1,048,576 bytes, although it is also used less technically to refer to a million bytes. Other numerical prefixes are interpreted similarly. With data transmission rates (measured in bits per second), a bit is considered as a signal pulse, and calculations are generally based on powers of ten. Thus, a rate of one megabit per second is equal to one million bits per second. However, in certain technical contexts, megabit can also refer to 1,048,576 bits. Similarly, the prefix kilo- refers to 1,000 or 210 (1,024); giga- to 1,000,000,000 (one billion) or 230 (1,073,741,824); and tera- to 1,000,000,000,000 (one trillion) or 240 (1,099,511,627,776).
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
megabyte [(meg-uh-beyet)]

A unit of computer information: one million bytes.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Computing Dictionary

megabyte definition

(MB, colloquially "meg") 2^20 = 1,048,576 bytes = 1024 kilobytes. 1024 megabytes are one gigabyte.
The text of a six hundred page paperback book would require about a megabyte of ASCII storage.
See prefix.

The Free On-line Dictionary of Computing, © Denis Howe 2010
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Example sentences
Every megabyte used after your limit will cost a nickel.
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