Conversion from Kibibits per second to Megaoctets 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.

Information about the Megaoctet per second (Mo/s)

The megaoctet per second is a unit of data transfer rate equal to one million octets per second, or eight megabits per second. Its symbol is Mo/s. It is the unit in which storage devices and their interfaces are rated, and the one a file manager shows while a copy is running.

Storage speeds fall naturally into this range. A mechanical hard drive sustains 100 to 250 megaoctets per second on sequential reads. A solid-state drive on the older interface reaches about 550, which is the limit of that interface rather than of the drive. A modern drive on the faster interface reaches several thousand, at which point the unit gives way to gigaoctets per second.

Interface speeds tell the same story from the other side. The successive versions of the universal serial bus have offered roughly 1.5, 60, 625 and 2,500 megaoctets per second at their nominal rates, and memory card standards have followed a similar path. A device is always limited by whichever of the two is slower, and matching them is the practical art of building a fast system.

For everyday sizes, one megaoctet per second transfers a photograph in a couple of seconds and a two-gigaoctet film in about half an hour. At 500 megaoctets per second the same film takes four seconds. That contrast explains why the perceived speed of a computer changed so completely when solid-state storage replaced mechanical drives, even though processors improved far less over the same period.

Sequential rates like these are the best case. Reading many small files instead of one large one costs far more, because each file requires locating its data and reading its record. A drive that sustains 500 megaoctets per second in sequence may manage only a few tens when copying a directory of thousands of small files, and that is where the difference between drive technologies is most visible.

The unit also describes the throughput of a busy network connection: a gigabit link delivers 125 megaoctets per second at best, so a fast local network and a fast drive are now comparable, and neither is obviously the limiting factor in a transfer.

One megaoctet per second equals 1,000,000 octets per second, 8 megabits per second, or about 0.9537 mebioctets per second.