| Yottabits (Ybit) | Zebioctets (Zio) |
|---|---|
| 1 Yottabit | 105.879118407 Zio |
| 2 Yottabits | 211.758236814 Zio |
| 3 Yottabits | 317.63735522 Zio |
| 4 Yottabits | 423.516473627 Zio |
| 5 Yottabits | 529.395592034 Zio |
| 10 Yottabits | 1058.79118407 Zio |
| 20 Yottabits | 2117.58236814 Zio |
| 25 Yottabits | 2646.97796017 Zio |
| 50 Yottabits | 5293.95592034 Zio |
| 100 Yottabits | 10587.9118407 Zio |
| Reference | Yottabits (Ybit) | Zebioctets (Zio) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-21 Ybit | 1.35525 × 10-19 Zio |
| A three-minute MP3 | 2.4 × 10-17 Ybit | 2.5411 × 10-15 Zio |
| A smartphone photo | 3.2 × 10-17 Ybit | 3.38813 × 10-15 Zio |
| A high-definition film | 3.2 × 10-14 Ybit | 3.38813 × 10-12 Zio |
| A dual-layer Blu-ray disc | 4 × 10-13 Ybit | 4.23516 × 10-11 Zio |
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 zebioctet is a unit of digital information equal to two to the seventieth power octets, which is 1,024 exbioctets. Its symbol is Zio. It is the binary counterpart of the zettaoctet, and the two differ by 18.1 per cent.
Nothing of this size exists. The total quantity of data held by humanity, counting every copy and every backup, is estimated in the low hundreds of zettaoctets, and a zebioctet is 1.18 zettaoctets, so the world holds a few hundred of these units in total. It is the first binary unit for which the world's entire stock is a small multiple rather than a large one.
The unit is defined for completeness rather than for use, which is a deliberate feature of both the metric and the IEC systems. Every prefix applies to every unit without exception, so a reader who has never seen Zio can decode it from the prefix alone. A system that ran out of names at some arbitrary point would force each future user to invent an extension, and rival extensions are how ambiguity is born.
There is one place where the unit would arise naturally. Storage addressing beyond 64 bits has been designed but not needed: the ZFS filesystem uses 128-bit block pointers, giving it a theoretical capacity far beyond any binary prefix that has a name. Where such a scheme states intermediate limits, those limits fall in this range and are properly written in zebioctets.
The 18.1 per cent gap between zebioctet and zettaoctet is worth holding in mind when reading forecasts. Predictions of global data growth are published in zettaoctets, and any that were computed in binary and reported in decimal are nearly a fifth off. Given that such forecasts are already rough, that error is not the largest source of uncertainty, but it is an avoidable one.
The symbol Zio, like all the IEC symbols, is a capital letter followed by lowercase i and then the unit. It is the presence of that i, rather than any statement in the text, that tells a reader unambiguously which quantity is meant, and a document that omits it has not said what it appears to have said.
One zebioctet equals 1,024 exbioctets, 1,180,591,620,717,411,303,424 octets, 8 zebibits, or about 1.181 zettaoctets.