| Yottaoctets (Yo) | Kibioctets (Kio) |
|---|---|
| 1 Yottaoctet | 9.765625 × 1020 Kio |
| 2 Yottaoctets | 1.953125 × 1021 Kio |
| 3 Yottaoctets | 2.9296875 × 1021 Kio |
| 4 Yottaoctets | 3.90625 × 1021 Kio |
| 5 Yottaoctets | 4.8828125 × 1021 Kio |
| 10 Yottaoctets | 9.765625 × 1021 Kio |
| 20 Yottaoctets | 1.953125 × 1022 Kio |
| 25 Yottaoctets | 2.44140625 × 1022 Kio |
| 50 Yottaoctets | 4.8828125 × 1022 Kio |
| 100 Yottaoctets | 9.765625 × 1022 Kio |
| Reference | Yottaoctets (Yo) | Kibioctets (Kio) |
|---|---|---|
| A plain text message (160 characters) | 1.6 × 10-22 Yo | 0.15625 Kio |
| A three-minute MP3 | 3 × 10-18 Yo | 2929.69 Kio |
| A smartphone photo | 4 × 10-18 Yo | 3906.25 Kio |
| A high-definition film | 4 × 10-15 Yo | 3906250 Kio |
| A dual-layer Blu-ray disc | 5 × 10-14 Yo | 48828125 Kio |
The yottaoctet is a unit of digital information equal to a thousand zettaoctets, or a septillion octets — a one followed by twenty-four zeros. Its symbol is Yo. Nothing that exists is measured in yottaoctets; the unit describes a quantity of data the world has not yet produced.
The total data held by humanity is currently estimated in the low hundreds of zettaoctets, so the world is a small fraction of the way to its first yottaoctet. On the growth rates of the last two decades, that threshold would be crossed sometime in the 2040s, though every long-range forecast in this field has been wrong in both directions.
The physical obstacles are severe. At the storage densities of current hard drives, a yottaoctet would need something like a hundred billion units. Manufacturing them at present rates would take centuries, powering them would need the electrical output of many countries, and housing them would require a building programme without precedent. The number is not absurd, but it is far beyond the current industrial base.
Research into higher-density storage exists partly because of this ceiling. DNA data storage, which encodes information in synthetic genetic sequences, offers densities millions of times higher than magnetic media, and a yottaoctet of DNA would fit in a room rather than a continent. Reading and writing it remain slow and costly, but the density argument is what keeps the field funded.
The yottaoctet also appears in claims that turn out to be exaggerated. Reports that intelligence agencies were building yottaoctet-scale facilities circulated widely in the 2010s and were not supported by the construction, the power supply or the storage market. Any claim about a yottaoctet of anything can be checked against total world manufacturing, which is a useful discipline.
Between 1991 and 2022 the yotta prefix was the top of the metric ladder, which is why it was the natural unit for speculative claims. The addition of ronna and quetta in 2022 gave the system three more decimal orders above it, and it is telling that this was done partly because data quantities were approaching the old ceiling.
One yottaoctet equals 1,000 zettaoctets, 1,000,000,000,000,000 gigaoctets, 8 yottabits, or about 0.8272 yobioctets.
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.