Conversion from Megaoctets per second to Kilooctets 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 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.