| Megaoctets (Mo) | Zebioctets (Zio) |
|---|---|
| 1 Megaoctet | 8.47032947254 × 10-16 Zio |
| 2 Megaoctets | 1.69406589451 × 10-15 Zio |
| 3 Megaoctets | 2.54109884176 × 10-15 Zio |
| 4 Megaoctets | 3.38813178902 × 10-15 Zio |
| 5 Megaoctets | 4.23516473627 × 10-15 Zio |
| 10 Megaoctets | 8.47032947254 × 10-15 Zio |
| 20 Megaoctets | 1.69406589451 × 10-14 Zio |
| 25 Megaoctets | 2.11758236814 × 10-14 Zio |
| 50 Megaoctets | 4.23516473627 × 10-14 Zio |
| 100 Megaoctets | 8.47032947254 × 10-14 Zio |
| Reference | Megaoctets (Mo) | Zebioctets (Zio) |
|---|---|---|
| A plain text message (160 characters) | 0.00016 Mo | 1.35525 × 10-19 Zio |
| A three-minute MP3 | 3 Mo | 2.5411 × 10-15 Zio |
| A smartphone photo | 4 Mo | 3.38813 × 10-15 Zio |
| A high-definition film | 4000 Mo | 3.38813 × 10-12 Zio |
| A dual-layer Blu-ray disc | 50000 Mo | 4.23516 × 10-11 Zio |
The megaoctet is a unit of digital information equal to one million octets, or eight million bits. Its symbol is Mo. It is the unit of the individual file: a photograph, a song, a document, an application download are all sized in megaoctets, which makes it the most frequently read data unit in daily life.
The typical figures are worth carrying in the head. A photograph from a phone is 2 to 5 megaoctets, a raw photograph from a system camera 25 to 50. A compressed song is 3 to 10. A minute of high-definition video is around 100. A long text document is under one. An operating system update is several thousand, which is why it is quoted in gigaoctets instead.
The megaoctet also carries the most notorious unit error in computing history. The 1.44 MB floppy disc holds neither 1.44 million octets nor 1.44 times 1,048,576. Its capacity is 1,440 kibioctets, which is 1,474,560 octets — the manufacturers multiplied a binary kilo by a decimal thousand and produced a figure that is correct in no system at all. It remains the standard illustration of why the IEC prefixes were needed.
Compact discs are cleaner: a standard disc holds about 700 megaoctets of data, or 74 to 80 minutes of audio, and that capacity was the practical limit for distributing software for a decade. Before them, distributing a program meant a box of floppies, and after them a DVD held about 4.7 gigaoctets, nearly seven times as much.
Memory sizes reached megaoctets in the early 1990s and stayed there for a decade. Four megaoctets was a comfortable amount in 1993 and inadequate by 1998, which tracks the arrival of graphical interfaces and the web. Today a single browser tab routinely holds more memory than an entire computer of that era.
The decimal-binary gap matters at this scale. A megaoctet is a million octets, but a mebioctet is 1,048,576, and a file reported as 100 MB by one program may appear as 95.4 MB in another. The difference is 4.9 per cent, small enough to overlook and large enough to cause arguments about whether a download completed correctly.
One megaoctet equals 1,000,000 octets, 1,000 kilooctets, 8 megabits, or about 0.9537 mebioctets.
The zebioctet is a unit of digital information equal to two to the seventieth power octets, which is 1,024 exbioctets. Its symbol is Zio. It is the binary counterpart of the zettaoctet, and the two differ by 18.1 per cent.
Nothing of this size exists. The total quantity of data held by humanity, counting every copy and every backup, is estimated in the low hundreds of zettaoctets, and a zebioctet is 1.18 zettaoctets, so the world holds a few hundred of these units in total. It is the first binary unit for which the world's entire stock is a small multiple rather than a large one.
The unit is defined for completeness rather than for use, which is a deliberate feature of both the metric and the IEC systems. Every prefix applies to every unit without exception, so a reader who has never seen Zio can decode it from the prefix alone. A system that ran out of names at some arbitrary point would force each future user to invent an extension, and rival extensions are how ambiguity is born.
There is one place where the unit would arise naturally. Storage addressing beyond 64 bits has been designed but not needed: the ZFS filesystem uses 128-bit block pointers, giving it a theoretical capacity far beyond any binary prefix that has a name. Where such a scheme states intermediate limits, those limits fall in this range and are properly written in zebioctets.
The 18.1 per cent gap between zebioctet and zettaoctet is worth holding in mind when reading forecasts. Predictions of global data growth are published in zettaoctets, and any that were computed in binary and reported in decimal are nearly a fifth off. Given that such forecasts are already rough, that error is not the largest source of uncertainty, but it is an avoidable one.
The symbol Zio, like all the IEC symbols, is a capital letter followed by lowercase i and then the unit. It is the presence of that i, rather than any statement in the text, that tells a reader unambiguously which quantity is meant, and a document that omits it has not said what it appears to have said.
One zebioctet equals 1,024 exbioctets, 1,180,591,620,717,411,303,424 octets, 8 zebibits, or about 1.181 zettaoctets.