Conversion from Tebibits per second to Megabits per second

Information about the Tebibit per second (Tibit/s)

The tebibit per second is a unit of data transfer rate equal to 1,099,511,627,776 bits per second, which is 1,024 gibibits per second. Its symbol is Tibit/s. It is the binary counterpart of the terabit per second, and the two differ by 10 per cent.

Ten per cent is the point at which the distinction becomes a matter of money rather than of pedantry. A supplier quoting a system at a hundred terabits per second and a customer measuring a hundred tebibits per second are not describing the same performance, and the difference is ten terabits — more than most organisations' entire external connectivity.

The rate belongs to the interior of very large machines. The aggregate memory bandwidth of a rack of accelerators, or the internal switching capacity of a large network chip, reaches this range, and both are built from power-of-two structures: memory channels of fixed binary width, switch ports in powers of two, buffers sized in binary. Expressing their totals with binary prefixes preserves the arithmetic that produced them.

In octets a tebibit per second is 137,438,953,472, or 128 gibioctets per second. That is more than any single storage device can supply and more than any external cable carries. It is a figure that describes something happening inside a cabinet, between chips connected by short traces on a board, where the physical distance is measured in centimetres.

Optical research also brushes this range. A laboratory demonstration carrying a petabit per second down one fibre is a thousand times higher, but individual wavelength channels and the electronics driving them work at tebibit-scale aggregates, and papers reporting them often state the binary figure because the underlying frame sizes are binary.

The habit of writing the lowercase i is worth keeping even where the reader is unlikely to check. A number written unambiguously can be converted correctly by anyone who reads it later; one written ambiguously cannot be repaired, and at ten per cent the ambiguity is no longer harmless.

One tebibit per second equals 1,024 gibibits per second, 137,438,953,472 octets per second, or about 1.100 terabits per second.

Information about the Megabit per second (Mbit/s)

The megabit per second is a unit of data transfer rate equal to one million bits per second. Its symbol is Mbit/s, often written Mbps. It is the unit in which internet connections are sold, which makes it the data unit most people encounter by name.

Because it is a decimal million and not 1,048,576, the conversion to octets is exact and easy: one megabit per second is 125 kilooctets per second, so a hundred-megabit connection delivers about 12.5 megaoctets per second at best. Anyone who watches a file transfer and does the division has understood the entire relationship between how connections are advertised and how transfers are reported.

What a household actually needs is far below what it usually buys. Standard-definition video streaming uses about 3 megabits per second, high definition about 5, and ultra-high definition about 25. A video call is around 3 to 8. A large family watching four separate high-definition streams while somebody downloads a game is using perhaps 60 megabits per second, which a hundred-megabit connection handles comfortably.

The reason to buy more capacity than that is not peak speed but behaviour under load. A link that is near its limit develops queues, and queues add delay, which shows up as stutter in video calls and lag in games. A connection with generous headroom keeps its latency low, and that is a more noticeable improvement than a higher number on a speed test.

Wired local networks pass through this range on the way up. The original Ethernet ran at 10 megabits per second, its successor at 100, and both were the standard office connection for a decade each before gigabit replaced them. Wireless standards followed the same path with a lag, and both are now measured in hundreds of megabits or in gigabits.

Real throughput is always below the nominal rate. Protocol overhead takes 5 to 10 per cent on a wired link; a shared wireless channel loses much more, because the medium is divided between all the devices using it and interference forces retransmission. A connection advertised at 100 megabits per second measured at 90 over cable and 50 over a busy wireless network is behaving normally.

One megabit per second equals 1,000,000 bits per second, 125 kilooctets per second, or about 0.9537 mebibits per second.