| Megaoctets (Mo) | Exbibits (Eibit) |
|---|---|
| 1 Megaoctet | 6.93889390391 × 10-12 Eibit |
| 2 Megaoctets | 1.38777878078 × 10-11 Eibit |
| 3 Megaoctets | 2.08166817117 × 10-11 Eibit |
| 4 Megaoctets | 2.77555756156 × 10-11 Eibit |
| 5 Megaoctets | 3.46944695195 × 10-11 Eibit |
| 10 Megaoctets | 6.93889390391 × 10-11 Eibit |
| 20 Megaoctets | 1.38777878078 × 10-10 Eibit |
| 25 Megaoctets | 1.73472347598 × 10-10 Eibit |
| 50 Megaoctets | 3.46944695195 × 10-10 Eibit |
| 100 Megaoctets | 6.93889390391 × 10-10 Eibit |
| Reference | Megaoctets (Mo) | Exbibits (Eibit) |
|---|---|---|
| A plain text message (160 characters) | 0.00016 Mo | 1.11022 × 10-15 Eibit |
| A three-minute MP3 | 3 Mo | 2.08167 × 10-11 Eibit |
| A smartphone photo | 4 Mo | 2.77556 × 10-11 Eibit |
| A high-definition film | 4000 Mo | 0.0000000277556 Eibit |
| A dual-layer Blu-ray disc | 50000 Mo | 0.000000346945 Eibit |
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 exbibit is a unit of digital information equal to two to the sixtieth power bits, which is 1,024 pebibits. Its symbol is Eibit. It is the binary counterpart of the exabit, and the two now differ by 15.3 per cent.
Two to the sixtieth is a number with a particular importance in computing, because sixty is close to the sixty-four bits of a modern processor address. A 64-bit machine can address sixteen exbioctets of memory, and that figure — 16 EiB — is the theoretical ceiling of the entire architecture. It appears in processor manuals, in operating system documentation and in the specification of every 64-bit filesystem.
No machine comes close to using that range. Current processors implement only forty-eight or fifty-seven of those sixty-four address bits, because wiring the full width would cost silicon for an address space nobody can fill. The unused bits are reserved, and widening the implementation is a straightforward matter whenever memory sizes make it worthwhile, which is the point of having chosen sixty-four in the first place.
An exbibit is 144,115,188,075,855,872 octets, or 128 pebioctets. That is more storage than any single organisation holds, and comparable to the combined annual output of a large part of the storage industry. As with all the larger binary units, it describes limits and capacities in specifications rather than anything that has been built.
The unit is also where filesystem designers set their maximum sizes. Filesystems built around 64-bit block pointers naturally have limits at exact powers of two, and several widely deployed ones specify maximum volume sizes in exbioctets. Those numbers are not aspirations; they are the arithmetic consequence of the pointer width, and they will hold until the architecture changes.
Reading the symbol correctly matters here. Eibit is the exbibit; Ebit is the exabit; EB and EiB are the octet forms of each. In a document where a fifteen per cent difference is significant — and at this scale it always is — the presence or absence of the lowercase i carries the entire meaning.
One exbibit equals 1,024 pebibits, 144,115,188,075,855,872 octets, or about 1.153 exabits.