| Yottabits (Ybit) | Yobioctets (Yio) |
|---|---|
| 1 Yottabit | 0.103397576569 Yio |
| 2 Yottabits | 0.206795153138 Yio |
| 3 Yottabits | 0.310192729707 Yio |
| 4 Yottabits | 0.413590306277 Yio |
| 5 Yottabits | 0.516987882846 Yio |
| 10 Yottabits | 1.03397576569 Yio |
| 20 Yottabits | 2.06795153138 Yio |
| 25 Yottabits | 2.58493941423 Yio |
| 50 Yottabits | 5.16987882846 Yio |
| 100 Yottabits | 10.3397576569 Yio |
| Reference | Yottabits (Ybit) | Yobioctets (Yio) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-21 Ybit | 1.32349 × 10-22 Yio |
| A three-minute MP3 | 2.4 × 10-17 Ybit | 2.48154 × 10-18 Yio |
| A smartphone photo | 3.2 × 10-17 Ybit | 3.30872 × 10-18 Yio |
| A high-definition film | 3.2 × 10-14 Ybit | 3.30872 × 10-15 Yio |
| A dual-layer Blu-ray disc | 4 × 10-13 Ybit | 4.1359 × 10-14 Yio |
The yottabit is a unit of digital information equal to a thousand zettabits — a one followed by twenty-four zeros. Its symbol is Ybit. For thirty years it was the largest unit the metric system offered, and it describes a quantity of data that does not yet exist anywhere.
A yottabit is 125 zettaoctets. The total of all data held by humanity is currently estimated in the low hundreds of zettaoctets, so the world's entire stock of information is somewhere around one or two yottabits. It is the first data unit that is genuinely larger than the thing it might describe, which is what makes it interesting.
The prefix yotta was adopted in 1991 at the 19th General Conference on Weights and Measures, alongside zetta. The names were invented rather than derived: the Greek and Latin numerals had been used up by peta and exa, and the committee needed letters that were not already taken as unit symbols. Y and Z were among the few remaining, and the syllables were built around them.
For a long time the yotta prefix marked the top of the ladder, and it appeared mainly in speculation and in claims about intelligence agencies' storage plans that turned out to be exaggerated. Then in 2022 the General Conference added ronna and quetta above it, together with ronto and quecto below, because data quantities were rising fast enough that the top was in sight.
Reaching a yottaoctet of storage with current technology would be a physical undertaking. Even at the highest densities available, it would require hundreds of millions of the largest hard drives ever made, a power supply comparable to that of a small country, and a building programme lasting decades. The constraint is not the mathematics but the silicon and the electricity.
The unit is nevertheless properly defined and a converter must handle it, both because forecasts of future data growth are written in yottaoctets and because the metric system's rule is that every prefix applies to every unit. A quantity does not need to exist for its name to be well formed.
One yottabit equals 1,000 zettabits, 125 zettaoctets, or about 0.8272 yobibits.
The yobioctet is a unit of digital information equal to two to the eightieth power octets, which is 1,024 zebioctets. Its symbol is Yio. It is the largest binary unit the International Electrotechnical Commission has named, and the binary counterpart of the yottaoctet.
At this final step the binary and decimal conventions differ by 20.9 per cent. That is the end of the argument the IEC prefixes were created to settle: a difference that began as a harmless 2.4 per cent at the kibioctet has grown, by eight successive multiplications of 1.024, into a discrepancy of more than a fifth. No system of measurement can carry an ambiguity that large.
A yobioctet is 1,208,925,819,614,629,174,706,176 octets. The entire quantity of data held by humanity is a few hundred zettaoctets, which is a fraction of a per cent of this. Nothing of this size has been built, and current manufacturing rates would need to continue for many centuries to accumulate one.
The binary series stops at yobi because the decimal series stopped at yotta when the IEC standard was written in 1998. When ronna and quetta were added to the metric system in 2022, no matching binary names were defined, so a quantity of two to the ninetieth octets has no accepted short form. That gap will presumably be filled if it is ever needed.
The value of defining the top of a ladder nobody has climbed is the same as the value of defining the bottom. A measurement system whose names run out forces its users to improvise, and improvised extensions conflict. Both the metric and the IEC series were written out in full so that the rule, rather than a table of exceptions, is all anyone has to learn.
For any reader of technical material, the lesson of the whole series is one character. Kio, Mio, Gio, Tio, Pio, Eio, Zio and Yio are binary; ko, Mo, Go, To, Po, Eo, Zo and Yo are decimal; and the difference between them widens from a rounding error to a fifth as you climb. That lowercase i is the only thing in a document that says which was meant.
One yobioctet equals 1,024 zebioctets, 1,208,925,819,614,629,174,706,176 octets, 8 yobibits, or about 1.209 yottaoctets.