| Kibioctets per second (Kio/s) | Yottaoctets per second (Yo/s) |
|---|---|
| 1 Kibioctet per second | 1.024 × 10-21 Yo/s |
| 2 Kibioctets per second | 2.048 × 10-21 Yo/s |
| 3 Kibioctets per second | 3.072 × 10-21 Yo/s |
| 4 Kibioctets per second | 4.096 × 10-21 Yo/s |
| 5 Kibioctets per second | 5.12 × 10-21 Yo/s |
| 10 Kibioctets per second | 1.024 × 10-20 Yo/s |
| 20 Kibioctets per second | 2.048 × 10-20 Yo/s |
| 25 Kibioctets per second | 2.56 × 10-20 Yo/s |
| 50 Kibioctets per second | 5.12 × 10-20 Yo/s |
| 100 Kibioctets per second | 1.024 × 10-19 Yo/s |
| Reference | Kibioctets per second (Kio/s) | Yottaoctets per second (Yo/s) |
|---|---|---|
| A dial-up modem | 6.83594 Kio/s | 7 × 10-21 Yo/s |
| Typical home broadband | 12207 Kio/s | 1.25 × 10-17 Yo/s |
| Gigabit Ethernet | 122070 Kio/s | 1.25 × 10-16 Yo/s |
| Streaming a 4K film | 3051.76 Kio/s | 3.125 × 10-18 Yo/s |
The kibioctet per second is a unit of data transfer rate equal to 1,024 octets per second, and therefore to 8,192 bits per second. Its symbol is Kio/s. Unlike most of the binary rate units it is genuinely common, because the command-line tools that copy, download and synchronise files have reported in it for decades.
The reason is straightforward. Those tools count what they have moved in blocks, and blocks are powers of two. A program that reads in four-kibioctet pieces and divides the total by elapsed time produces a rate in kibioctets per second, and reporting it in decimal kilooctets would require an extra multiplication for no benefit. The unit is what the arithmetic naturally produces.
Anyone who has watched a file copy on a Unix-like system has seen the figure. Download utilities, archive tools, disc-writing commands and network file transfer programs all report progress in kibioctets or mebioctets per second, and most of them label it correctly with the lowercase i. It is one of the few places where the IEC prefixes are used consistently in everyday software.
For scale, a kibioctet per second moves about a thousand characters of text each second: a short letter in a second, a novel in about ten minutes. It is a rate at which a modern web page will not load in any reasonable time, so seeing it in a progress display usually means something has gone wrong with the connection rather than that the transfer is nearly finished.
The difference from a kilooctet per second is 2.4 per cent, which nobody notices. The value of using the binary unit here is not accuracy but honesty: the number came from a binary computation, and writing it with a binary prefix says so. A reader who wants the decimal figure can convert; a reader given a decimal label for a binary number cannot recover anything.
Comparing the reading with an advertised connection speed requires two steps: multiply by eight to get bits, and adjust by 2.4 per cent for the base. In practice the second step is beneath the noise of any real measurement, and the first is the one that matters.
One kibioctet per second equals 1,024 octets per second, 8,192 bits per second, or 1.024 kilooctets per second.
The yottaoctet per second is a unit of data transfer rate equal to a thousand zettaoctets per second, or eight yottabits per second. Its symbol is Yo/s. It is the largest transfer rate the metric system named for thirty years, and it stands at the point where the question stops being one of engineering and becomes one of physics.
The physical limits are real and can be stated. Any communication channel has a capacity set by its bandwidth and its signal-to-noise ratio, a result Claude Shannon proved in 1948. Pushing a rate higher means using more bandwidth, more power, or more parallel channels, and each of those has a cost that grows without limit as the rate does.
Energy sets the sharpest bound. Thermodynamics requires a minimum energy to distinguish one state from another at a given temperature, and although practical systems are many orders of magnitude above that floor, the floor is not zero. At a yottaoctet per second even the theoretical minimum becomes a substantial power, and every real system multiplies it by a large factor.
There is also a limit from the medium itself. A single optical fibre has a capacity ceiling set by non-linear effects in the glass, which grow with the light power carried, so raising the power eventually degrades the signal rather than improving it. Reaching a yottaoctet per second would require something like a hundred billion fibres running at today's records simultaneously, which is a construction problem rather than a communication one.
None of this makes the unit meaningless. It is properly defined, it converts by the same rule as every other, and it appears in discussions of theoretical limits and in complete tables of the prefix system. A measurement system that stopped naming quantities at the point where engineering stops would be less useful, not more.
Since 2022 the metric system has had ronna and quetta above yotta, so this is no longer the top of the ladder. That extension was driven by data quantities rather than by rates, and nothing in transmission has yet given a reason to write a rate above this one.
One yottaoctet per second equals 1,000 zettaoctets per second, 8 yottabits per second, or about 0.8272 yobioctets per second.