| Zettabits (Zbit) | Exabits (Ebit) |
|---|---|
| 1 Zettabit | 1000 Ebit |
| 2 Zettabits | 2000 Ebit |
| 3 Zettabits | 3000 Ebit |
| 4 Zettabits | 4000 Ebit |
| 5 Zettabits | 5000 Ebit |
| 10 Zettabits | 10000 Ebit |
| 20 Zettabits | 20000 Ebit |
| 25 Zettabits | 25000 Ebit |
| 50 Zettabits | 50000 Ebit |
| 100 Zettabits | 100000 Ebit |
| Reference | Zettabits (Zbit) | Exabits (Ebit) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-18 Zbit | 1.28 × 10-15 Ebit |
| A three-minute MP3 | 2.4 × 10-14 Zbit | 2.4 × 10-11 Ebit |
| A smartphone photo | 3.2 × 10-14 Zbit | 3.2 × 10-11 Ebit |
| A high-definition film | 3.2 × 10-11 Zbit | 0.000000032 Ebit |
| A dual-layer Blu-ray disc | 4 × 10-10 Zbit | 0.0000004 Ebit |
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 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.