A megabit is a unit of information or computer storage, abbreviated Mbit (or Mb).
1 megabit = 106 = 1,000,000 bits which is equal to 125,000 bytes. In kilobytes this is either 125 kB (decimal meaning) or about 122 kB (122 KiB) (binary meaning).
The megabit is most commonly used when referring to data transfer rates in network speeds, e.g. a 100 Mbit/s (megabit per second) Fast Ethernet connection. In this context, like elsewhere in telecommunications, it always equals 106 bits. Residential high speed internet access is often advertised incorrectly in megabits (a unit of information) rather than megabit per second.
A binary counterpart of the megabit, the mebibit, refers to the binary quantity 10242 bits. Standard industry practice in RAM and ROM manufacture is to use the Mb abbreviation in reference to this binary quantity. For example, a single discrete DDR3 chip specified at 512Mb invariably contains exactly 229 bits = 536,870,912 bits = 512 Mibit of storage,
or 67,108,864 8-bit bytes, variously referred to as either 64 mebibytes or (debatable) 64 megabytes.
Video game cartridges
In the 16-bit games console era, the 'megabit' became a commonly-used measure of the size (computer data storage
capacity) of games cartridges. This "megabit" actually equals one mebibit
(Mibit). The vast majority of SNES
and Sega Mega Drive
(Genesis) games were produced on standard 8 megabit cartridges, although 4 megabit cartridges were not uncommon and, later in the life of these consoles, graphically-intensive titles would appear on 12, 16, even 32 megabit cartridges. Tales of Phantasia
and Star Ocean
were 48 megabit. Chrono Trigger
was a 32 megabit cartridge game.
The actual rule is: 8 bits = 1 byte. Therefore a 4 megabit cartridge had a capacity of 512 KiB, an 8 megabit cartridge held 1 MiB of data, and so on.