Conversion from Megaoctets per second to 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.

Information about the Kilobit per second (kbit/s)

The kilobit per second is a unit of data transfer rate equal to one thousand bits per second. Its symbol is kbit/s, often written kbps. It was the unit of the dial-up era, and it survives today as the unit in which audio and speech encoding rates are quoted.

The dial-up sequence is worth recalling because each number marks a technical generation. Modems ran at 300 bits per second in the late 1970s, then 1,200, 2,400, 9,600, 14,400, 28,800, 33,600 and finally 56 kilobits per second at the end of the 1990s. That last figure was the ceiling of an ordinary telephone line, set by the eight-kilohertz sampling of the digital telephone network rather than by the modem.

Audio encoding is where the unit now lives. Telephone-quality speech runs at 8 to 64 kilobits per second depending on the codec, with modern low-rate codecs producing intelligible speech at 8 and high-quality voice calls at 24 to 32. Music at 128 kilobits per second was the early standard of portable players, 192 and 256 are common, and 320 is the practical ceiling of the older lossy formats.

Those numbers reward a moment of arithmetic. Music at 128 kilobits per second is 16 kilooctets per second, so a four-minute track is about 3.8 megaoctets. Uncompressed compact-disc audio runs at 1,411 kilobits per second, so the compressed file is about a tenth the size of the original, which is the whole point of the format.

Video subtitle streams, control channels and telemetry links also work in kilobits per second. So does much of the machine-to-machine traffic that fills modern networks: a sensor reporting a reading every few seconds needs a fraction of a kilobit per second, and the protocols designed for such devices are built around keeping the radio switched off most of the time.

The unit's lower-case k marks the decimal kilo, one thousand exactly. In transmission this has never been ambiguous, because network rates have always been counted in true thousands; the binary confusion that afflicts storage units does not arise here, and a kilobit per second means the same thing in every document.

One kilobit per second equals 1,000 bits per second, 125 octets per second, or about 0.9766 kibibits per second.