| Terabits (Tbit) | Yottabits (Ybit) |
|---|---|
| 1 Terabit | 1 × 10-12 Ybit |
| 2 Terabits | 2 × 10-12 Ybit |
| 3 Terabits | 3 × 10-12 Ybit |
| 4 Terabits | 4 × 10-12 Ybit |
| 5 Terabits | 5 × 10-12 Ybit |
| 10 Terabits | 1 × 10-11 Ybit |
| 20 Terabits | 2 × 10-11 Ybit |
| 25 Terabits | 2.5 × 10-11 Ybit |
| 50 Terabits | 5 × 10-11 Ybit |
| 100 Terabits | 1 × 10-10 Ybit |
| Reference | Terabits (Tbit) | Yottabits (Ybit) |
|---|---|---|
| A plain text message (160 characters) | 0.00000000128 Tbit | 1.28 × 10-21 Ybit |
| A three-minute MP3 | 0.000024 Tbit | 2.4 × 10-17 Ybit |
| A smartphone photo | 0.000032 Tbit | 3.2 × 10-17 Ybit |
| A high-definition film | 0.032 Tbit | 3.2 × 10-14 Ybit |
| A dual-layer Blu-ray disc | 0.4 Tbit | 4 × 10-13 Ybit |
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 yottabit is a unit of digital information equal to a thousand zettabits — a one followed by twenty-four zeros. Its symbol is Ybit. For thirty years it was the largest unit the metric system offered, and it describes a quantity of data that does not yet exist anywhere.
A yottabit is 125 zettaoctets. The total of all data held by humanity is currently estimated in the low hundreds of zettaoctets, so the world's entire stock of information is somewhere around one or two yottabits. It is the first data unit that is genuinely larger than the thing it might describe, which is what makes it interesting.
The prefix yotta was adopted in 1991 at the 19th General Conference on Weights and Measures, alongside zetta. The names were invented rather than derived: the Greek and Latin numerals had been used up by peta and exa, and the committee needed letters that were not already taken as unit symbols. Y and Z were among the few remaining, and the syllables were built around them.
For a long time the yotta prefix marked the top of the ladder, and it appeared mainly in speculation and in claims about intelligence agencies' storage plans that turned out to be exaggerated. Then in 2022 the General Conference added ronna and quetta above it, together with ronto and quecto below, because data quantities were rising fast enough that the top was in sight.
Reaching a yottaoctet of storage with current technology would be a physical undertaking. Even at the highest densities available, it would require hundreds of millions of the largest hard drives ever made, a power supply comparable to that of a small country, and a building programme lasting decades. The constraint is not the mathematics but the silicon and the electricity.
The unit is nevertheless properly defined and a converter must handle it, both because forecasts of future data growth are written in yottaoctets and because the metric system's rule is that every prefix applies to every unit. A quantity does not need to exist for its name to be well formed.
One yottabit equals 1,000 zettabits, 125 zettaoctets, or about 0.8272 yobibits.