One megatonne of TNT equivalent amounts to approx. 4 petajoules and is the approximate energy released on igniting one million tonnes of TNT. The unit is often used in measuring the explosive power of nuclear weapons.
In some fields of computing, mega may sometimes denote 1,048,576 (220) of information units, for example, a megabyte, a megaword, but denotes 1000000 (106) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi- has been suggested as a prefix for 220 to avoid ambiguity.
^"Oxford English Dictionary (OED Online)". www.oed.com (3rd ed.). Oxford University Press. June 2001. Retrieved 2017-09-18. (Subscription required (help)). Origin: A borrowing from Greek. Etymon: Greek μεγα-. ... Forming scientific and technical terms with the sense ‘very large’, ‘comparatively large’, or (esp. in Pathol.) ‘abnormally large’, often having correlatives beginning micro-, and sometimes also synonyms beginning macro-.