| Terabits (Tbit) | Zettaoctets (Zo) |
|---|---|
| 1 Terabit | 1.25 × 10-10 Zo |
| 2 Terabits | 2.5 × 10-10 Zo |
| 3 Terabits | 3.75 × 10-10 Zo |
| 4 Terabits | 5 × 10-10 Zo |
| 5 Terabits | 6.25 × 10-10 Zo |
| 10 Terabits | 0.00000000125 Zo |
| 20 Terabits | 0.0000000025 Zo |
| 25 Terabits | 0.000000003125 Zo |
| 50 Terabits | 0.00000000625 Zo |
| 100 Terabits | 0.0000000125 Zo |
| Reference | Terabits (Tbit) | Zettaoctets (Zo) |
|---|---|---|
| A plain text message (160 characters) | 0.00000000128 Tbit | 1.6 × 10-19 Zo |
| A three-minute MP3 | 0.000024 Tbit | 3 × 10-15 Zo |
| A smartphone photo | 0.000032 Tbit | 4 × 10-15 Zo |
| A high-definition film | 0.032 Tbit | 4 × 10-12 Zo |
| A dual-layer Blu-ray disc | 0.4 Tbit | 5 × 10-11 Zo |
The terabit is a unit of digital information equal to one million million bits, a thousand gigabits. Its symbol is Tbit. It is the scale at which the internet's own infrastructure is measured — not the connection into a house, but the links between cities and across oceans.
A terabit is 125 gigaoctets. Put another way, one terabit is roughly the amount of data in a hundred and twenty-five hours of high-definition video, or the contents of a large laptop's disc. A single terabit-per-second link therefore moves the equivalent of that laptop every second, continuously.
Submarine cables are where these numbers live. A modern transoceanic cable carries several hundred terabits per second across a handful of fibre pairs, using wavelength division multiplexing to run dozens of separate light channels down the same glass strand at once. The cables laid across the Atlantic in the 2020s reach into the hundreds of terabits, where the first transatlantic telephone cable of 1956 carried thirty-six voice calls.
Internet exchange points, where networks meet and hand traffic to one another, publish their throughput in terabits per second. The largest in Europe and Asia peak in the tens of terabits, and those figures are among the most reliable public measurements of how much the internet is actually being used at a given moment.
Laboratory records go far higher. Research teams have pushed single optical fibres past a petabit per second by using multi-core fibre and hundreds of wavelengths simultaneously, though such experiments run over short distances under controlled conditions. The gap between what is demonstrated in a laboratory and what is deployed in the sea is usually about a decade.
For storage the terabit is used mainly in the semiconductor industry, where the density of a memory die is quoted in terabits per square centimetre or per package. Consumer products are labelled in octets instead — a terabit is 125 gigaoctets, so a chip described as 8 terabits appears on the shelf as a one-teraoctet drive.
One terabit equals 1,000,000,000,000 bits, 1,000 gigabits, 125 gigaoctets, or about 0.9095 tebibits.
The zettaoctet is a unit of digital information equal to a thousand exaoctets, or a sextillion octets. Its symbol is Zo. It is the unit in which the total quantity of data in the world is now described, and the only data unit that has given its name to an era.
That name came from the phrase the zettabyte era, used from around 2016, when annual global internet traffic first exceeded one zettaoctet. Estimates of the global datasphere — every file stored anywhere, plus everything created and immediately discarded — passed a hundred zettaoctets a few years later and continue to rise by tens of zettaoctets a year.
Understanding what these figures include matters more than the numbers themselves. They count copies. A single photograph on a phone is also on the phone's backup, on two servers in a cloud provider's data centre, in a caching layer, and possibly in a machine learning training set. Counting stored octets rather than distinct works inflates the total by a large factor that nobody has ever measured precisely.
The composition of the total is dominated by things nobody looks at. Surveillance and security video, most of it overwritten within weeks, is the single largest category. Sensor and telemetry data from industrial equipment, vehicles and buildings is second. Human-authored material of any kind is a minority, and text is a rounding error within that minority.
Manufacturing sets a hard limit on the total. All the world's storage factories together produce a few hundred exaoctets of new capacity per year, which is a fraction of a zettaoctet, so most data created is never stored at all. It is processed as it arrives and thrown away, and this is a deliberate design choice rather than a failure.
For a sense of the scale, a zettaoctet would be about eight thousand million large consumer hard drives, or roughly one for every person on Earth. Stacked flat, that many drives would form a column reaching well beyond the Moon. The unit describes a quantity that only exists as a sum across a whole planet's industry.
One zettaoctet equals 1,000 exaoctets, 1,000,000,000,000 gigaoctets, 8 zettabits, or about 0.8470 zebioctets.