| Kibibits per second (Kibit/s) | Pebioctets per second (Pio/s) |
|---|---|
| 1 Kibibit per second | 1.13686837722 × 10-13 Pio/s |
| 2 Kibibits per second | 2.27373675443 × 10-13 Pio/s |
| 3 Kibibits per second | 3.41060513165 × 10-13 Pio/s |
| 4 Kibibits per second | 4.54747350886 × 10-13 Pio/s |
| 5 Kibibits per second | 5.68434188608 × 10-13 Pio/s |
| 10 Kibibits per second | 1.13686837722 × 10-12 Pio/s |
| 20 Kibibits per second | 2.27373675443 × 10-12 Pio/s |
| 25 Kibibits per second | 2.84217094304 × 10-12 Pio/s |
| 50 Kibibits per second | 5.68434188608 × 10-12 Pio/s |
| 100 Kibibits per second | 1.13686837722 × 10-11 Pio/s |
| Reference | Kibibits per second (Kibit/s) | Pebioctets per second (Pio/s) |
|---|---|---|
| A dial-up modem | 54.6875 Kibit/s | 6.21725 × 10-12 Pio/s |
| Typical home broadband | 97656.2 Kibit/s | 0.0000000111022 Pio/s |
| Gigabit Ethernet | 976562 Kibit/s | 0.000000111022 Pio/s |
| Streaming a 4K film | 24414.1 Kibit/s | 0.00000000277556 Pio/s |
The kibibit per second is a unit of data transfer rate equal to 1,024 bits per second. Its symbol is Kibit/s. It is the binary counterpart of the kilobit per second, and it is the least used member of an already unusual family, because transfer rates are one of the few places in computing where the decimal convention has always been unambiguous.
Networking has counted in true thousands from the beginning. A modem rated at 56 kilobits per second meant fifty-six thousand, not fifty-seven thousand three hundred and forty-four. The reason is that a transmission rate is set by a clock, and clocks are specified in decimal frequencies: a link running at ten million symbols per second carries a decimal number of bits, not a power of two.
The binary prefixes exist for quantities, not for rates, because quantities of storage are organised in powers of two while time is not. There is no natural reason for a rate to be a power of two, and consequently no reason for a rate unit to need a binary prefix. Where one appears, it is almost always because a program divided a binary file size by a duration.
That is exactly where the kibibit per second does turn up. A tool that measures a transfer by counting kibioctets and dividing by seconds produces a rate in kibioctets per second, and multiplying by eight gives kibibits per second. The unit is a consequence of the arithmetic rather than a description of the channel.
For scale, a kibibit per second is 128 octets per second, and the difference from a kilobit per second is 2.4 per cent — smaller than the measurement error of almost any real throughput test. At this level the distinction is technically correct and practically invisible, which is a fair description of the whole binary prefix system at its lower end.
The unit is properly defined and a converter must handle it, because the IEC series applies to every unit without exception. Whether anyone writes it is a separate question from whether it means something definite, and it does.
One kibibit per second equals 1,024 bits per second, 128 octets per second, or 1.024 kilobits per second.
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.