| Teraoctets (To) | Yottabits (Ybit) |
|---|---|
| 1 Teraoctet | 8 × 10-12 Ybit |
| 2 Teraoctets | 1.6 × 10-11 Ybit |
| 3 Teraoctets | 2.4 × 10-11 Ybit |
| 4 Teraoctets | 3.2 × 10-11 Ybit |
| 5 Teraoctets | 4 × 10-11 Ybit |
| 10 Teraoctets | 8 × 10-11 Ybit |
| 20 Teraoctets | 1.6 × 10-10 Ybit |
| 25 Teraoctets | 2 × 10-10 Ybit |
| 50 Teraoctets | 4 × 10-10 Ybit |
| 100 Teraoctets | 8 × 10-10 Ybit |
| Reference | Teraoctets (To) | Yottabits (Ybit) |
|---|---|---|
| A plain text message (160 characters) | 1.6 × 10-10 To | 1.28 × 10-21 Ybit |
| A three-minute MP3 | 0.000003 To | 2.4 × 10-17 Ybit |
| A smartphone photo | 0.000004 To | 3.2 × 10-17 Ybit |
| A high-definition film | 0.004 To | 3.2 × 10-14 Ybit |
| A dual-layer Blu-ray disc | 0.05 To | 4 × 10-13 Ybit |
The teraoctet is a unit of digital information equal to one million million octets, or a thousand gigaoctets. Its symbol is To. It is the unit of the modern hard drive, and the point at which personal storage stopped being something anyone needed to manage carefully.
A teraoctet holds roughly two hundred and fifty thousand photographs from a phone, or two hundred hours of high-definition video, or a quarter of a million songs. For a person who is not a professional photographer or video editor, a single teraoctet is more storage than a lifetime of ordinary files will fill.
Consumer hard drives crossed one teraoctet in 2007 and now reach twenty or more. Solid-state drives arrived at the same capacities more slowly and at higher cost, but with far greater speed, and the two technologies now divide the market between capacity and performance rather than competing directly.
The teraoctet is where the decimal-binary discrepancy becomes visible enough to annoy. A drive sold as one teraoctet holds a million million octets exactly; the operating system divides by 1,024 four times and reports 0.909 tebioctets, which it usually labels as 931 gigaoctets. The shortfall appears to be 7 per cent, though nothing has actually been lost. At the petaoctet the same arithmetic produces a 12 per cent gap.
Backup and archiving live at this scale. A household's complete collection of photographs, documents and video typically fits in a few teraoctets, which is why external drives are sold in exactly that range. Cloud storage services price in teraoctets too, and the economics of keeping a second copy of everything only work because the unit price of storage has fallen faster than the quantity has grown.
In professional work the teraoctet is a daily quantity rather than a milestone. A day of filming in high resolution produces several teraoctets of raw footage. A genome sequencing run produces a few hundred gigaoctets, so a modest laboratory generates teraoctets a week. Both fields have had to build workflows around moving data that will not fit on any network in reasonable time.
One teraoctet equals 1,000,000,000,000 octets, 1,000 gigaoctets, 8 terabits, or about 0.9095 tebioctets.
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.