| Yottabits (Ybit) | Exbioctets (Eio) |
|---|---|
| 1 Yottabit | 108420.217249 Eio |
| 2 Yottabits | 216840.434497 Eio |
| 3 Yottabits | 325260.651746 Eio |
| 4 Yottabits | 433680.868994 Eio |
| 5 Yottabits | 542101.086243 Eio |
| 10 Yottabits | 1084202.17249 Eio |
| 20 Yottabits | 2168404.34497 Eio |
| 25 Yottabits | 2710505.43121 Eio |
| 50 Yottabits | 5421010.86243 Eio |
| 100 Yottabits | 10842021.7249 Eio |
| Reference | Yottabits (Ybit) | Exbioctets (Eio) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-21 Ybit | 1.38778 × 10-16 Eio |
| A three-minute MP3 | 2.4 × 10-17 Ybit | 2.60209 × 10-12 Eio |
| A smartphone photo | 3.2 × 10-17 Ybit | 3.46945 × 10-12 Eio |
| A high-definition film | 3.2 × 10-14 Ybit | 0.00000000346945 Eio |
| A dual-layer Blu-ray disc | 4 × 10-13 Ybit | 0.0000000433681 Eio |
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 exbioctet is a unit of digital information equal to two to the sixtieth power octets, which is 1,024 pebioctets. Its symbol is Eio. It is the binary counterpart of the exaoctet, and the two differ by 15.3 per cent.
One number involving this unit is quoted more than any other: sixteen exbioctets, the size of the address space a 64-bit processor can reach. Two to the sixty-fourth octets is 16 EiB, and that figure is the theoretical ceiling on the memory of every machine built on the architecture that has dominated computing since the mid-2000s.
The same limit reappears in filesystems. A filesystem that numbers its blocks with 64-bit values can address 16 exbioctets of blocks, and several modern designs state exactly that as their maximum volume size. Others state 8 exbioctets, having reserved one bit for a sign or a flag — a detail that halves the limit and is worth knowing when reading a specification.
Nothing approaches these sizes in practice. The largest storage systems in the world hold exaoctets, and the total of all data held by humanity is a few hundred zettaoctets, which is tens of thousands of exbioctets. The 64-bit ceiling was chosen precisely so that it would not be reached, and the transition from 32 bits, whose four-gibioctet limit was reached within a decade, is why the designers left so much room.
An exbioctet is 1,152,921,504,606,846,976 bits and 128 pebioctets. It is a quantity that exists in specifications, in address arithmetic and in the design documents of large systems, and nowhere else. Describing it in terms of photographs or films is not useful, because no collection of either comes close.
The symbol Eio and its decimal sibling Eo differ by more than an eighth, which is far too much to leave to inference. When a document writes EB in the context of an address space, it almost certainly means EiB, because address spaces are powers of two by construction; when it writes EB about stored data, it almost certainly means the decimal unit.
One exbioctet equals 1,024 pebioctets, 1,152,921,504,606,846,976 octets, 8 exbibits, or about 1.153 exaoctets.