| Exaoctets (Eo) | Kibioctets (Kio) |
|---|---|
| 1 Exaoctet | 976562500000000 Kio |
| 2 Exaoctets | 1.953125 × 1015 Kio |
| 3 Exaoctets | 2.9296875 × 1015 Kio |
| 4 Exaoctets | 3.90625 × 1015 Kio |
| 5 Exaoctets | 4.8828125 × 1015 Kio |
| 10 Exaoctets | 9.765625 × 1015 Kio |
| 20 Exaoctets | 1.953125 × 1016 Kio |
| 25 Exaoctets | 2.44140625 × 1016 Kio |
| 50 Exaoctets | 4.8828125 × 1016 Kio |
| 100 Exaoctets | 9.765625 × 1016 Kio |
| Reference | Exaoctets (Eo) | Kibioctets (Kio) |
|---|---|---|
| A plain text message (160 characters) | 1.6 × 10-16 Eo | 0.15625 Kio |
| A three-minute MP3 | 3 × 10-12 Eo | 2929.69 Kio |
| A smartphone photo | 4 × 10-12 Eo | 3906.25 Kio |
| A high-definition film | 0.000000004 Eo | 3906250 Kio |
| A dual-layer Blu-ray disc | 0.00000005 Eo | 48828125 Kio |
The exaoctet is a unit of digital information equal to a thousand petaoctets, or a billion gigaoctets. Its symbol is Eo. It is the unit in which the world's data flows and stockpiles are counted, and it belongs to civilisations rather than to companies or machines.
The most quoted figure involving it is global internet traffic, which passed one exaoctet per month around 2004 and now runs to several hundred exaoctets monthly. Written as an annual total that is several thousand exaoctets, which is why the zettaoctet was pressed into service for yearly figures a decade ago.
A frequently repeated claim holds that all the words ever spoken by human beings would amount to about five exaoctets in text. The estimate comes from a 2003 study and is very rough, but it makes the point: five exaoctets is now less than a fortnight of internet traffic. Whatever the exact number, the flow of data through the network long ago overtook the total of everything humanity has ever said.
Storage at exaoctet scale exists only at the largest cloud providers, and even there it is spread across dozens of buildings on several continents. The annual production of all the world's hard drives and flash memory together is a few hundred exaoctets, so the exaoctet is also the natural unit for describing the output of an entire industry.
What is stored at this scale is mostly not what people imagine. Backups, replicas, logs, telemetry, machine learning training corpora and video kept for regulatory reasons dominate. Deliberately created human work — documents, photographs, recordings that someone chose to make and keep — is a small and shrinking fraction of the whole.
The prefix exa has been part of the metric system since 1975, adopted at the same conference as peta. At the time these were prefixes without applications, defined for completeness. The fact that both became working units of a commercial industry within thirty years is the clearest single measure of how quickly digital information grew.
One exaoctet equals 1,000 petaoctets, 1,000,000,000 gigaoctets, 8 exabits, or about 0.8674 exbioctets.
The kibioctet is a unit of digital information equal to 1,024 octets, and therefore to 8,192 bits. Its symbol is Kio. It is the binary counterpart of the kilooctet, and although the two differ by only 2.4 per cent, this is the unit in which a great deal of a computer's internal organisation is actually measured.
The most important example is the memory page. Processors do not manage memory octet by octet but in fixed-size blocks, and on almost every architecture in common use that block is 4 kibioctets. Every allocation a program makes is rounded up to a multiple of that, every entry in the page tables describes one of them, and the performance of a program often depends on how well its access pattern fits that four-kibioctet grid.
Disc sectors tell a similar story. Hard drives used 512-octet sectors for decades, and modern drives use 4 kibioctets, matching the memory page so that a page can be read or written in a single operation. Filesystems then allocate space in blocks that are themselves powers of two, usually 4 kibioctets, which is why a one-octet file consumes four kibioctets of disc.
Network protocols use the unit too. Buffer sizes, window sizes and the maximum size of many protocol structures are powers of two, and the 64-kibioctet limit appears repeatedly: it is the largest value a 16-bit length field can express, and it therefore caps the size of a UDP datagram, an IP packet and several older file formats.
That is the general pattern: wherever a limit comes from the width of a binary field, the limit is a power of two, and the honest way to write it is with a binary prefix. Writing 64 KB for the datagram limit is not wrong by much, but writing 64 KiB is exactly right and says where the number came from.
In everyday use the difference is invisible. A 200-kilooctet file and a 200-kibioctet file are 4.8 kibioctets apart, which nobody notices. The value of the distinction is that it makes the arithmetic behind a figure legible, which matters far more as the numbers grow.
One kibioctet equals 1,024 octets, 8,192 bits, 8 kibibits, or 1.024 kilooctets.