Conversion from Mebibits per second to Kilooctets 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 Kilooctet per second (ko/s)

The kilooctet per second is a unit of data transfer rate equal to one thousand octets per second, and therefore to eight kilobits per second. Its symbol is ko/s. It is the unit in which file transfers were reported through the whole of the dial-up era, and it still appears whenever a transfer is slow enough to need it.

The conversion from advertised connection speeds is the reason it matters. A 56-kilobit modem delivered about 7 kilooctets per second in practice, and users learned the relationship by watching progress bars: a one-megaoctet file took about two and a half minutes. The habit of dividing the advertised number by eight and then subtracting a bit for overhead dates from that period.

Storage devices of the era were similar. A floppy disc drive read at roughly 30 to 60 kilooctets per second, a single-speed compact-disc drive at 150, and an early hard drive at a few hundred. Loading a program from any of them was a matter of seconds to minutes, and software was written with that expectation in mind.

The unit still appears in serial communication. The classic serial port ran at rates up to 115,200 bits per second, which is 14.4 kilooctets per second, and equivalent rates are still used to talk to microcontrollers, scientific instruments and industrial equipment. A protocol designed for such a link cannot assume that a large message will arrive quickly.

It also appears at the bottom end of modern networking. A congested mobile connection, a distant satellite link or a heavily shared wireless network can fall to a few tens of kilooctets per second, and at that rate an ordinary web page — which now runs to a few megaoctets — takes a minute or more to load. The unit is a reminder of what the network assumes about its users.

For scale, one kilooctet per second moves a thousand characters of plain text each second, so a short letter transfers in a second and a novel in about ten minutes. Nothing about text has ever needed more than this; every increase in transfer rate since has been consumed by images, sound and video.

One kilooctet per second equals 1,000 octets per second, 8 kilobits per second, or about 0.9766 kibioctets per second.