| Pebioctets per second (Pio/s) | Octets per second (octet/s) |
|---|---|
| 1 Pebioctet per second | 1.12589990684 × 1015 octet/s |
| 2 Pebioctets per second | 2.25179981369 × 1015 octet/s |
| 3 Pebioctets per second | 3.37769972053 × 1015 octet/s |
| 4 Pebioctets per second | 4.50359962737 × 1015 octet/s |
| 5 Pebioctets per second | 5.62949953421 × 1015 octet/s |
| 10 Pebioctets per second | 1.12589990684 × 1016 octet/s |
| 20 Pebioctets per second | 2.25179981369 × 1016 octet/s |
| 25 Pebioctets per second | 2.81474976711 × 1016 octet/s |
| 50 Pebioctets per second | 5.62949953421 × 1016 octet/s |
| 100 Pebioctets per second | 1.12589990684 × 1017 octet/s |
| Reference | Pebioctets per second (Pio/s) | Octets per second (octet/s) |
|---|---|---|
| A dial-up modem | 6.21725 × 10-12 Pio/s | 7000 octet/s |
| Typical home broadband | 0.0000000111022 Pio/s | 12500000 octet/s |
| Gigabit Ethernet | 0.000000111022 Pio/s | 125000000 octet/s |
| Streaming a 4K film | 0.00000000277556 Pio/s | 3125000 octet/s |
The pebioctet per second is a unit of data transfer rate equal to 1,024 tebioctets per second, or two to the fiftieth power octets per second. Its symbol is Pio/s. It is the binary counterpart of the petaoctet per second, and the two differ by 12.6 per cent.
The rate exists only as a total. The aggregate memory bandwidth of a whole supercomputer, or the summed capacity of the network fabric joining its cabinets, reaches this range, and both are sums over tens of thousands of components, each of which moves a few hundred gibioctets per second on its own.
Whether such a total means anything depends on the calculation being run. A problem that divides so that each node works mostly on its own data can use the full aggregate. A problem where every node must constantly consult every other cannot, and the machine's effective bandwidth falls to what the slowest shared path allows. Most of the art of parallel programming lies in getting problems into the first category.
In octets a pebioctet per second is 1,125,899,906,842,624, and in decimal terms about 1.126 petaoctets per second. The 12.6 per cent difference is the accumulated effect of five multiplications by 1.024, and it is now large enough that no report can leave the convention unstated without introducing real uncertainty.
The unit also appears in descriptions of parallel filesystems at the largest facilities, where a storage system spread across tens of thousands of drives delivers a few pebioctets per second to a compute cluster. That number determines how quickly the machine can checkpoint its state, which in turn determines how much work is lost when a component fails — and in a machine of that size, something is always failing.
For a converter the requirement is simply that the arithmetic be exact and the label preserved. Multiplying by 1,024 five times is not difficult; silently substituting the decimal prefix is the error to avoid.
One pebioctet per second equals 1,024 tebioctets per second, 1,125,899,906,842,624 octets per second, or about 1.126 petaoctets per second.
The octet per second is a unit of data transfer rate equal to eight bits per second. Its symbol is octet/s. It is the unit in which software reports transfer speeds, as against the bits per second in which hardware and network services advertise them, and the factor of eight between the two conventions is the source of endless confusion.
The division of labour is consistent once it is understood. Anything describing a physical link — an Ethernet port, a fibre connection, a radio channel, a broadband package — is quoted in bits per second, because bits are what the signalling actually carries. Anything describing a file moving from one place to another is quoted in octets per second, because files are measured in octets.
A download manager that reports 12 megaoctets per second on a connection sold as 100 megabits per second is not disagreeing with the advertisement; it is stating the same rate in the other convention, and the arithmetic between them is a division by eight. Recognising this immediately removes the most common cause of complaint about internet speed.
Individual octets per second appear in the same narrow places as individual bits: deep-space telemetry, low-power sensor links, and the slowest legacy serial connections. A rate of a hundred octets per second would move a page of text in about twenty seconds, which was a normal experience in the 1970s and is unimaginable now.
The unit also underlies the way disc and interface throughput is described. A drive that sustains 500 megaoctets per second is moving four gigabits per second across its interface, and matching the two figures is a routine part of system design: an interface rated in gigabits must be compared with a drive rated in octets, and the factor of eight decides whether one starves the other.
Storage tools reinforce the convention. Every file copy utility, backup program and command-line transfer tool reports in octets per second or its multiples, and every network measurement tool reports in bits per second. A person reading both at once has to keep the conversion in mind, which is exactly what makes the distinction worth stating explicitly.
One octet per second equals 8 bits per second, 0.008 kilobits per second, or 0.001 kilooctets per second.