Conversion from 25 Terabits per second to Petaoctets per second

Information about the Terabit per second (Tbit/s)

The terabit per second is a unit of data transfer rate equal to a thousand gigabits per second. Its symbol is Tbit/s. It is the unit of the internet's backbone: the submarine cables, the exchange points and the long-haul optical links that carry traffic between continents.

A single modern transoceanic cable carries several hundred terabits per second. It achieves this not with one enormous channel but with wavelength division multiplexing, which sends dozens of separate colours of light down each fibre at once, and with several fibre pairs in the same cable. Each wavelength carries a few hundred gigabits, and the totals add up.

The historical comparison is worth stating plainly. The first transatlantic telephone cable, laid in 1956, carried thirty-six simultaneous voice calls. A cable laid in the 2020s carries hundreds of terabits per second, enough for hundreds of millions of simultaneous calls. That is a factor of roughly ten million in seventy years, and it was achieved almost entirely by changing what is sent down the glass rather than by laying more cable.

Internet exchange points, where networks meet and hand traffic to one another, publish their throughput in terabits per second. The largest in Europe and Asia peak in the tens of terabits, and those public graphs are among the most reliable measurements of how heavily the internet is being used at a given moment, because they count real traffic rather than capacity.

In octets, a terabit per second is 125 gigaoctets per second — the contents of a large laptop's disc moved every second, continuously. No single storage system can feed such a link; the traffic on these routes is the aggregate of millions of separate connections, each of them tiny by comparison.

Laboratory records go far higher, into petabits per second, using multi-core fibre and hundreds of wavelengths at once, though over short distances under controlled conditions. The gap between what is demonstrated in a laboratory and what is deployed under an ocean has historically been about a decade.

One terabit per second equals 1,000 gigabits per second, 125 gigaoctets per second, or about 0.9095 tebibits per second.

Information about the Petaoctet per second (Po/s)

The petaoctet per second is a unit of data transfer rate equal to a thousand teraoctets per second, or eight petabits per second. Its symbol is Po/s. It describes the total internal bandwidth of the largest computing machines rather than any single connection, and it exists as an aggregate rather than as a rate anything can sustain on its own.

The clearest case is the interconnect of an exascale supercomputer. Such a machine has tens of thousands of nodes, each linked to the network at hundreds of gigaoctets per second, and the sum across the whole fabric reaches petaoctets per second. That figure is the reason such machines can run a single calculation spread over the whole system rather than many small independent ones.

Memory bandwidth adds up the same way. A machine with ten thousand accelerators, each with several teraoctets per second of local memory bandwidth, has tens of petaoctets per second in total. Whether that total means anything depends entirely on the calculation: a problem that can be divided so each node works mostly on its own data can use it, and a problem that cannot, cannot.

Data centre networks reach this range too. The aggregate capacity of the switching fabric inside a very large facility, counting every link between every rack, is measured in petaoctets per second. The design goal is that any server can reach any other at close to full speed, which requires far more internal capacity than the facility's external connections.

For scale, a petaoctet per second would transfer the entire contents of a large national archive in a second, or fill every hard drive manufactured in a day within about a minute. No storage system can supply data at this rate, and none can absorb it; the number describes movement inside a machine, between memory and processors, where nothing is being stored at all.

The unit also serves in optical research, where a single fibre carrying a petabit per second is 125 teraoctets per second, and an experimental system aggregating several such fibres approaches the petaoctet. Those figures come from laboratories rather than from anything deployed.

One petaoctet per second equals 1,000 teraoctets per second, 8 petabits per second, or about 0.8882 pebioctets per second.