Megabit

The megabit is a multiple of the unit bit for digital information. The prefix mega (symbol M) is defined in the International System of Units (SI) as a multiplier of 106 (1 million),[1] and therefore

1 megabit = 106bits = 1000000bits = 1000 kilobits.
This article is about the unit of 106 bits. For the unit of 220 bits, see mebibit.
Not to be confused with megabyte.
Multiple-bit units
Decimal
Value  Metric 
1000 kbitkilobit
10002 Mbitmegabit
10003 Gbitgigabit
10004 Tbitterabit
10005 Pbitpetabit
10006 Ebitexabit
10007 Zbitzettabit
10008 Ybityottabit
10009 Rbitronnabit
100010 Qbitquettabit
Binary
Value  IEC  JEDEC 
1024 Kibitkibibit KbitKbkilobit
10242 Mibitmebibit MbitMbmegabit
10243 Gibitgibibit GbitGbgigabit
10244 Tibittebibit —
10245 Pibitpebibit —
10246 Eibitexbibit —
10247 Zibitzebibit —
10248 Yibityobibit —
—
—
Orders of magnitude of data

The megabit has the unit symbol Mbit or Mb. The lowercase 'b' in Mb distinguishes it from MB (for megabyte).

The megabit is closely related to the mebibit, a unit multiple derived from the binary prefix mebi (symbol Mi) of the same order of magnitude,[2] which is equal to 220bits = 1048576bits, or approximately 5% larger than the megabit. Despite the definitions of these new prefixes for binary-based quantities of storage by international standards organizations, memory semiconductor chips are still marketed using the metric prefix names to designate binary multiples.

Using the common byte size of eight bits and the standard decimal definition of megabit and kilobyte, 1 megabit is equal to 125 kilobytes (kB) or approximately 122 kibibytes (KiB).

The megabit is widely used when referring to data transfer rates of computer networks or telecommunications systems. Network transfer rates and download speeds often use the megabit as the amount transferred per time unit, e.g., a 100 Mbit/s (megabit per second) Fast-Ethernet connection, or a 10 Mbit/s Internet access service, whereas the sizes of data units (files) transferred over these networks are often measured in megabytes. To achieve a transfer rate of one megabyte per second one needs a network connection with a transfer rate of eight megabits per second.

Usage
  • In telecommunications, the base 10 definition of the unit (one million bits) is standard.
  • In the semiconductor industry, it is still common practice to designate random-access memory (RAM), read-only memory (ROM) in a binary interpretation of the metric prefixes, such as the megabit, so that one megabit represents 220bits=1048576bits.[3][4][5] For example, a single discrete DDR3 chip specified at "512 Mb" contains 229 bits = 536870912bits = 512 Mibit (approximately 536.87 Mbit) of storage,[6] or 671088648-bit bytes, variously referred to as either 64 mebibytes or 64 (binary) megabytes.
  • During the 16-bit game console era, the megabit (Mb) was a commonly used measure of the size (computer data storage capacity) of game cartridges. This size represented one mebibit (Mibit). The vast majority of SNES and Mega Drive (Genesis) games were produced on 8 megabit cartridges, although other sizes such as 4, 12, 16, 24, 32, and 48 Mb cartridges appeared. This usage continued on the Nintendo 64, with cartridge sizes ranging between 32 and 512 Mb.

References
  1. The NIST Reference on Constants, Units, and Uncertainty: SI prefixes
  2. The NIST Reference on Constants, Units, and Uncertainty: Prefixes for binary multiples
  3. "DDR3 SDRAM Memory Product Guide" (PDF). Samsung Global. Retrieved 12 February 2015.
  4. "S25FL128P Data Sheet" (PDF). Spansion Support. Retrieved 12 February 2015.
  5. "1-Megabit (128K x 8) Paged Parallel EEPROMs" (PDF). Atmel Corporation. Retrieved 12 February 2015.
  6. "JEDEC Standard DDR3 SDRAM Specification" (PDF, 8.8 MB). Retrieved 2008-07-10.
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