| Yottabits (Ybit) | Mebibits (Mibit) |
|---|---|
| 1 Yottabit | 9.53674316406 × 1017 Mibit |
| 2 Yottabits | 1.90734863281 × 1018 Mibit |
| 3 Yottabits | 2.86102294922 × 1018 Mibit |
| 4 Yottabits | 3.81469726562 × 1018 Mibit |
| 5 Yottabits | 4.76837158203 × 1018 Mibit |
| 10 Yottabits | 9.53674316406 × 1018 Mibit |
| 20 Yottabits | 1.90734863281 × 1019 Mibit |
| 25 Yottabits | 2.38418579102 × 1019 Mibit |
| 50 Yottabits | 4.76837158203 × 1019 Mibit |
| 100 Yottabits | 9.53674316406 × 1019 Mibit |
| Reference | Yottabits (Ybit) | Mebibits (Mibit) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-21 Ybit | 0.0012207 Mibit |
| A three-minute MP3 | 2.4 × 10-17 Ybit | 22.8882 Mibit |
| A smartphone photo | 3.2 × 10-17 Ybit | 30.5176 Mibit |
| A high-definition film | 3.2 × 10-14 Ybit | 30517.6 Mibit |
| A dual-layer Blu-ray disc | 4 × 10-13 Ybit | 381470 Mibit |
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.
The mebibit is a unit of digital information equal to 1,048,576 bits, which is 1,024 kibibits or two to the twentieth power. Its symbol is Mibit. It is the binary counterpart of the megabit, and the difference between the two has grown to 4.9 per cent — small enough to be ignored casually, large enough to matter in a specification.
Its natural home is semiconductor memory, where capacity is fixed by the address lines on the chip. A memory die with twenty address bits can reach exactly 1,048,576 locations, so densities land on powers of two rather than on round decimal numbers. A chip described as 512 megabits in a catalogue is very often 512 mebibits in reality, which is 537 megabits, and the datasheet is where the truth is written.
That habit is old and deliberate. Semiconductor manufacturers have always sized memory in binary because the wiring makes any other choice wasteful: an address bus is a fixed number of lines, and using only part of the range it can reach throws away silicon. Storage manufacturers had no such constraint, which is precisely why the two industries diverged.
For a sense of quantity, a mebibit is 131,072 octets, or about 128 kibioctets. That is roughly the contents of a long book as plain text, or a single low-resolution image. In network terms it is a hundredth of a second of a gigabit link.
The IEC prefixes were introduced in 1998 partly because at this level and above the approximation stops being safe. Buying a component described as one megabit and receiving one mebibit is a five per cent surprise; at the tebibit the same confusion is a ten per cent surprise, and in a contract for a data centre that is a real sum of money.
Correct usage is now common in standards documents, in hardware datasheets and in operating system internals, and rare in advertising and consumer software. The best rule when reading a figure is to ask which industry produced it: if it describes memory or a chip, assume binary; if it describes storage or a link, assume decimal.
One mebibit equals 1,048,576 bits, 1,024 kibibits, 131,072 octets, or about 1.049 megabits.