| Zebibits (Zibit) | Zebioctets (Zio) |
|---|---|
| 1 Zebibit | 0.125 Zio |
| 2 Zebibits | 0.25 Zio |
| 3 Zebibits | 0.375 Zio |
| 4 Zebibits | 0.5 Zio |
| 5 Zebibits | 0.625 Zio |
| 10 Zebibits | 1.25 Zio |
| 20 Zebibits | 2.5 Zio |
| 25 Zebibits | 3.125 Zio |
| 50 Zebibits | 6.25 Zio |
| 100 Zebibits | 12.5 Zio |
| Reference | Zebibits (Zibit) | Zebioctets (Zio) |
|---|---|---|
| A plain text message (160 characters) | 1.0842 × 10-18 Zibit | 1.35525 × 10-19 Zio |
| A three-minute MP3 | 2.03288 × 10-14 Zibit | 2.5411 × 10-15 Zio |
| A smartphone photo | 2.71051 × 10-14 Zibit | 3.38813 × 10-15 Zio |
| A high-definition film | 2.71051 × 10-11 Zibit | 3.38813 × 10-12 Zio |
| A dual-layer Blu-ray disc | 3.38813 × 10-10 Zibit | 4.23516 × 10-11 Zio |
The zebibit is a unit of digital information equal to two to the seventieth power bits, which is 1,024 exbibits. Its symbol is Zibit. It is the binary counterpart of the zettabit, and the two now differ by 18.1 per cent — nearly a fifth.
That divergence is the reason the binary prefixes were needed at all. At the kibibit the two conventions differed by 2.4 per cent, a rounding error. Here the difference is large enough that a document using the wrong one is simply reporting a different quantity, and no amount of context can repair the ambiguity after the fact.
A zebibit is 147,573,952,589,676,412,928 octets, or 128 exbioctets. Nothing of this size exists. The total data held by humanity is somewhere in the low hundreds of zettaoctets, which is under a zebioctet, so the world's entire information stock does not yet reach one unit at this step of the binary ladder.
The unit exists because the IEC series was defined completely rather than as far as anyone then needed. That is the same principle the metric system follows: every prefix applies to every unit, whether or not the combination has yet been used. A system with holes in it requires a table of exceptions, and a system without holes requires only the rule.
Where the zebibit could genuinely appear is in address space arithmetic. Two to the seventieth is not a natural pointer width, but multiples and fractions of powers of two run through every discussion of addressing, and a scheme that reserved seventy bits for something would naturally be described in these terms. Such schemes are proposed occasionally and none has yet been needed.
Reading the symbol is the practical skill. Zibit is binary, Zbit is decimal, and at eighteen per cent apart the two are not interchangeable in any document where the number matters. Where a source writes ZB with no explanation, there is no way to know which was meant, and the honest response is to treat the figure as uncertain to a fifth.
One zebibit equals 1,024 exbibits, 147,573,952,589,676,412,928 octets, or about 1.181 zettabits.
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.