| Exabits (Ebit) | Yobioctets (Yio) |
|---|---|
| 1 Exabit | 0.000000103397576569 Yio |
| 2 Exabits | 0.000000206795153138 Yio |
| 3 Exabits | 0.000000310192729707 Yio |
| 4 Exabits | 0.000000413590306277 Yio |
| 5 Exabits | 0.000000516987882846 Yio |
| 10 Exabits | 0.00000103397576569 Yio |
| 20 Exabits | 0.00000206795153138 Yio |
| 25 Exabits | 0.00000258493941423 Yio |
| 50 Exabits | 0.00000516987882846 Yio |
| 100 Exabits | 0.0000103397576569 Yio |
| Reference | Exabits (Ebit) | Yobioctets (Yio) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-15 Ebit | 1.32349 × 10-22 Yio |
| A three-minute MP3 | 2.4 × 10-11 Ebit | 2.48154 × 10-18 Yio |
| A smartphone photo | 3.2 × 10-11 Ebit | 3.30872 × 10-18 Yio |
| A high-definition film | 0.000000032 Ebit | 3.30872 × 10-15 Yio |
| A dual-layer Blu-ray disc | 0.0000004 Ebit | 4.1359 × 10-14 Yio |
The exabit is a unit of digital information equal to a thousand petabits, or a billion billion bits. Its symbol is Ebit. At this scale no device, no cable and no building is being described. The exabit measures the traffic of whole regions and the output of entire industries over stretches of time.
An exabit is 125 petaoctets. The most common place to meet the unit is in figures for global internet traffic, which are usually given in exaoctets per month. Worldwide traffic passed one exaoctet per month around 2004, reached about a hundred by 2017 and is now several hundred, which in bits is several thousand exabits every month.
Those totals divide in revealing ways. The overwhelming majority is video, and the rest is dominated by software updates, cloud synchronisation and machine-to-machine traffic rather than by anything a person is actively reading. A single popular film released simultaneously worldwide can move a measurable fraction of an exabit in a day.
Storage at this scale exists only as aggregates. The combined capacity of all the hard drives and flash memory manufactured in a year is measured in hundreds of exaoctets, which is thousands of exabits. Estimates of all the data held by humanity at any moment run into the tens of zettaoctets, and the exabit is the unit one step below that in which the components of such estimates are counted.
Scientific instruments produce exabit quantities before any of it is stored. The Square Kilometre Array radio telescope generates raw data at a rate that would fill exaoctets within days, and its design is built around discarding and summarising in real time rather than recording. The same is true of the large particle detectors and of high-resolution climate simulations.
The prefix exa comes from the Greek for six, the exabit being a thousand to the sixth power in bits. It was adopted in 1975 along with peta, at a time when no one expected either to describe anything but astronomical or theoretical quantities. Both are now ordinary units in the technology industry, which says something about how fast the numbers grew.
One exabit equals 1,000 petabits, 125 petaoctets, or about 0.8674 exbibits.
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.