| Exaoctets (Eo) | Yobioctets (Yio) |
|---|---|
| 1 Exaoctet | 0.000000827180612553 Yio |
| 2 Exaoctets | 0.00000165436122511 Yio |
| 3 Exaoctets | 0.00000248154183766 Yio |
| 4 Exaoctets | 0.00000330872245021 Yio |
| 5 Exaoctets | 0.00000413590306277 Yio |
| 10 Exaoctets | 0.00000827180612553 Yio |
| 20 Exaoctets | 0.0000165436122511 Yio |
| 25 Exaoctets | 0.0000206795153138 Yio |
| 50 Exaoctets | 0.0000413590306277 Yio |
| 100 Exaoctets | 0.0000827180612553 Yio |
| Reference | Exaoctets (Eo) | Yobioctets (Yio) |
|---|---|---|
| A plain text message (160 characters) | 1.6 × 10-16 Eo | 1.32349 × 10-22 Yio |
| A three-minute MP3 | 3 × 10-12 Eo | 2.48154 × 10-18 Yio |
| A smartphone photo | 4 × 10-12 Eo | 3.30872 × 10-18 Yio |
| A high-definition film | 0.000000004 Eo | 3.30872 × 10-15 Yio |
| A dual-layer Blu-ray disc | 0.00000005 Eo | 4.1359 × 10-14 Yio |
The exaoctet is a unit of digital information equal to a thousand petaoctets, or a billion gigaoctets. Its symbol is Eo. It is the unit in which the world's data flows and stockpiles are counted, and it belongs to civilisations rather than to companies or machines.
The most quoted figure involving it is global internet traffic, which passed one exaoctet per month around 2004 and now runs to several hundred exaoctets monthly. Written as an annual total that is several thousand exaoctets, which is why the zettaoctet was pressed into service for yearly figures a decade ago.
A frequently repeated claim holds that all the words ever spoken by human beings would amount to about five exaoctets in text. The estimate comes from a 2003 study and is very rough, but it makes the point: five exaoctets is now less than a fortnight of internet traffic. Whatever the exact number, the flow of data through the network long ago overtook the total of everything humanity has ever said.
Storage at exaoctet scale exists only at the largest cloud providers, and even there it is spread across dozens of buildings on several continents. The annual production of all the world's hard drives and flash memory together is a few hundred exaoctets, so the exaoctet is also the natural unit for describing the output of an entire industry.
What is stored at this scale is mostly not what people imagine. Backups, replicas, logs, telemetry, machine learning training corpora and video kept for regulatory reasons dominate. Deliberately created human work — documents, photographs, recordings that someone chose to make and keep — is a small and shrinking fraction of the whole.
The prefix exa has been part of the metric system since 1975, adopted at the same conference as peta. At the time these were prefixes without applications, defined for completeness. The fact that both became working units of a commercial industry within thirty years is the clearest single measure of how quickly digital information grew.
One exaoctet equals 1,000 petaoctets, 1,000,000,000 gigaoctets, 8 exabits, or about 0.8674 exbioctets.
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.