| Zettabits (Zbit) | Yobioctets (Yio) |
|---|---|
| 1 Zettabit | 0.000103397576569 Yio |
| 2 Zettabits | 0.000206795153138 Yio |
| 3 Zettabits | 0.000310192729707 Yio |
| 4 Zettabits | 0.000413590306277 Yio |
| 5 Zettabits | 0.000516987882846 Yio |
| 10 Zettabits | 0.00103397576569 Yio |
| 20 Zettabits | 0.00206795153138 Yio |
| 25 Zettabits | 0.00258493941423 Yio |
| 50 Zettabits | 0.00516987882846 Yio |
| 100 Zettabits | 0.0103397576569 Yio |
| Reference | Zettabits (Zbit) | Yobioctets (Yio) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-18 Zbit | 1.32349 × 10-22 Yio |
| A three-minute MP3 | 2.4 × 10-14 Zbit | 2.48154 × 10-18 Yio |
| A smartphone photo | 3.2 × 10-14 Zbit | 3.30872 × 10-18 Yio |
| A high-definition film | 3.2 × 10-11 Zbit | 3.30872 × 10-15 Yio |
| A dual-layer Blu-ray disc | 4 × 10-10 Zbit | 4.1359 × 10-14 Yio |
The zettabit is a unit of digital information equal to a thousand exabits, or a sextillion bits — a one followed by twenty-one zeros. Its symbol is Zbit. It is the largest unit in which real, measured quantities of data are still routinely reported, and it entered common use only in the last fifteen years.
A zettabit is 125 exaoctets. The phrase that made the prefix familiar was the zettabyte era, coined for the moment around 2016 when annual global internet traffic first exceeded one zettaoctet. That threshold arrived a little over a decade after annual traffic first passed one exaoctet, which gives a fair sense of the growth rate involved.
Estimates of the total quantity of data in existence are given in zettaoctets. The global datasphere — everything stored on every server, disc, phone and memory card, plus everything created and immediately discarded — is put at somewhere above a hundred zettaoctets, which is more than eight hundred zettabits. Nobody counts this directly; the figures come from manufacturing statistics and modelling.
Almost all of that is machine-generated and never read by anyone. Surveillance video that is recorded and overwritten, sensor telemetry, logs, backups and the many copies that redundancy demands account for the overwhelming majority. The portion that a human being has ever looked at is a tiny fraction of the total, and shrinking as a share every year.
The prefix zetta was adopted in 1991, along with yotta, at a conference that also had to consider what letters remained available. Z and Y were chosen partly because they were unused, and the pattern of naming from the Greek and Latin numerals had by then become loose. The 2022 additions of ronna and quetta continued the ladder upward for the same reason.
For perspective, a zettabit of information written as text in a single line of characters would stretch far beyond the solar system. The unit does not describe anything a person can hold or handle; it describes a civilisation's accumulated output, and it is useful precisely because that quantity now needs a name.
One zettabit equals 1,000 exabits, 125 exaoctets, or about 0.8470 zebibits.
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.