before vowels meg-, word-forming element often meaning "large, great," but in physics a precise measurement to denote the unit taken a million times (megaton, megawatt, etc.), from Greek megas "great, large, vast, big, high, tall; mighty, important" (fem. megale), from PIE root *meg- "great." Mega began to be used alone as an adjective by 1982.
"unit of digital information in a computer," typically consisting of eight bits, 1956, American English; see bit (n.2). Reputedly coined by German-born American computer scientist Werner Buchholz (b. 1922) at IBM.
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Harper, D. (n.d.). Etymology of megabyte. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/megabyte