Conversion from Mebibits per second to Kibibits per second

Information about the Mebibit per second (Mibit/s)

The mebibit per second is a unit of data transfer rate equal to 1,048,576 bits per second. Its symbol is Mibit/s. It is the binary counterpart of the megabit per second, and the two differ by 4.9 per cent — small, but large enough to change a headline figure.

That five per cent is where the unit starts to matter. A connection advertised at 100 megabits per second and a connection at 100 mebibits per second differ by about five megabits, which is a whole high-definition video stream. In a specification, a contract or a benchmark report, quoting one and delivering the other is a real discrepancy rather than a rounding difference.

In practice the confusion is rare in networking, because network equipment is always specified in decimal. What produces mebibit figures is measurement software: a tool that counts a transfer in mebioctets and divides by elapsed seconds is reporting a binary rate, and multiplying by eight makes it mebibits per second. A person comparing that reading with an advertised rate must convert twice, once for the base and once for the factor of eight.

Where a genuine binary rate does arise is inside a machine. A memory bus transfers a fixed number of bits per clock cycle, and the width is a power of two — sixty-four bits at a time, for instance — so the quantity moved per cycle is binary even though the clock frequency is not. Rates derived from such a structure are naturally expressed with binary prefixes.

For scale, a mebibit per second is 131,072 octets per second, or about 128 kibioctets per second. That is roughly a photograph every two seconds, or a plain-text novel every four. It is a rate at which the modern web is slow but usable, which puts it in the range that mobile networks fall to when congested.

The correct symbol has the lowercase i, and its presence is the only reliable way to tell the two conventions apart. A document writing Mbit/s in a context where the underlying figure came from a binary computation has misstated its own measurement by five per cent.

One mebibit per second equals 1,048,576 bits per second, 131,072 octets per second, or about 1.049 megabits per second.

Information about the Kibibit per second (Kibit/s)

The kibibit per second is a unit of data transfer rate equal to 1,024 bits per second. Its symbol is Kibit/s. It is the binary counterpart of the kilobit per second, and it is the least used member of an already unusual family, because transfer rates are one of the few places in computing where the decimal convention has always been unambiguous.

Networking has counted in true thousands from the beginning. A modem rated at 56 kilobits per second meant fifty-six thousand, not fifty-seven thousand three hundred and forty-four. The reason is that a transmission rate is set by a clock, and clocks are specified in decimal frequencies: a link running at ten million symbols per second carries a decimal number of bits, not a power of two.

The binary prefixes exist for quantities, not for rates, because quantities of storage are organised in powers of two while time is not. There is no natural reason for a rate to be a power of two, and consequently no reason for a rate unit to need a binary prefix. Where one appears, it is almost always because a program divided a binary file size by a duration.

That is exactly where the kibibit per second does turn up. A tool that measures a transfer by counting kibioctets and dividing by seconds produces a rate in kibioctets per second, and multiplying by eight gives kibibits per second. The unit is a consequence of the arithmetic rather than a description of the channel.

For scale, a kibibit per second is 128 octets per second, and the difference from a kilobit per second is 2.4 per cent — smaller than the measurement error of almost any real throughput test. At this level the distinction is technically correct and practically invisible, which is a fair description of the whole binary prefix system at its lower end.

The unit is properly defined and a converter must handle it, because the IEC series applies to every unit without exception. Whether anyone writes it is a separate question from whether it means something definite, and it does.

One kibibit per second equals 1,024 bits per second, 128 octets per second, or 1.024 kilobits per second.