Conversion from Megaoctets per second to Gigaoctets 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 Gigaoctet per second (Go/s)

The gigaoctet per second is a unit of data transfer rate equal to one thousand million octets per second, or eight gigabits per second. Its symbol is Go/s. It is the unit of the fastest storage devices and of the buses inside a computer, where data moves between processor, memory and drive.

Solid-state drives on the current interface reach 3 to 14 gigaoctets per second, depending on the number of lanes they use and the generation of the bus. Each lane of the peripheral interconnect provides roughly 2 gigaoctets per second at the current generation, and a drive typically uses four of them. Doubling the generation doubles the rate, which is why the figures have risen so steadily.

Main memory is faster still. A modern memory channel delivers 30 to 60 gigaoctets per second, and a machine with several channels reaches hundreds. Graphics processors, which must feed thousands of arithmetic units at once, use memory with bandwidths measured in thousands of gigaoctets per second, at which point the unit gives way to teraoctets.

That hierarchy is what determines how a program performs. A processor can execute far more operations per second than memory can supply data for, so most fast software is written to keep data in the small fast caches rather than to fetch it repeatedly from main memory. The whole discipline of performance engineering rests on the size of these differences.

For everyday comparison, one gigaoctet per second copies a two-gigaoctet film in two seconds, and fills a one-teraoctet drive in about seventeen minutes. That is faster than the network in almost every home and faster than most external connections, so at this rate the bottleneck moves back to whatever is at the other end.

The unit also describes network links in the data centre. A ten-gigabit connection is 1.25 gigaoctets per second, a hundred-gigabit connection 12.5, and both are common between servers. Comparing a storage figure in octets with a network figure in bits requires the factor of eight, and forgetting it is how equipment gets mismatched.

One gigaoctet per second equals 1,000,000,000 octets per second, 8 gigabits per second, or about 0.9313 gibioctets per second.