Mega is a unit prefix in metric systems of units denoting a factor of one million (106 or 1000000).
Mega comes from Ancient Greek: μέγας, romanized: mégas, lit. 'great'.
[1] When units occur in exponentiation, such as in square and cubic forms, any multiples-prefix is considered part of the unit, and thus included in the exponentiation.
In some fields of computing, mega may sometimes denote 1048576 (220) information units, for example, a megabyte, a megaword, but denotes 1000000 (106) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s.
In the case of 3½-inch floppy disks, sizes were given in megabytes of 1000KB or 1024000 bytes.