| Kilooctets (ko) | Yobibits (Yibit) |
|---|---|
| 1 Kilooctet | 6.61744490042 × 10-21 Yibit |
| 2 Kilooctets | 1.32348898008 × 10-20 Yibit |
| 3 Kilooctets | 1.98523347013 × 10-20 Yibit |
| 4 Kilooctets | 2.64697796017 × 10-20 Yibit |
| 5 Kilooctets | 3.30872245021 × 10-20 Yibit |
| 10 Kilooctets | 6.61744490042 × 10-20 Yibit |
| 20 Kilooctets | 1.32348898008 × 10-19 Yibit |
| 25 Kilooctets | 1.65436122511 × 10-19 Yibit |
| 50 Kilooctets | 3.30872245021 × 10-19 Yibit |
| 100 Kilooctets | 6.61744490042 × 10-19 Yibit |
| Reference | Kilooctets (ko) | Yobibits (Yibit) |
|---|---|---|
| A plain text message (160 characters) | 0.16 ko | 1.05879 × 10-21 Yibit |
| A three-minute MP3 | 3000 ko | 1.98523 × 10-17 Yibit |
| A smartphone photo | 4000 ko | 2.64698 × 10-17 Yibit |
| A high-definition film | 4000000 ko | 2.64698 × 10-14 Yibit |
| A dual-layer Blu-ray disc | 50000000 ko | 3.30872 × 10-13 Yibit |
The kilooctet is a unit of digital information equal to one thousand octets, and therefore to eight thousand bits. Its symbol is ko. It is the smallest of the everyday storage units, and for two decades it was the unit in which the whole capacity of a computer was described.
A kilooctet holds a thousand characters of unaccented text, which is about two hundred words, or a third of a page. The plain-text file of a short letter is a few kilooctets. Almost nothing else in modern computing is this small: an empty document from a word processor is already tens of kilooctets, because the file format carries formatting, fonts and metadata around the text.
The historical importance of the unit is hard to overstate. The Apple II shipped with 4 kilooctets of memory, the Commodore 64 was named for its 64, and the first IBM personal computer could address 640. Programs of real complexity — spreadsheets, word processors, games with graphics and sound — were written to fit inside those numbers, which required a discipline that has largely disappeared.
The kilooctet is also where the decimal and binary confusion began. Memory came in 1,024-octet units because addressing is binary, and everyone called that a kilooctet. Disc manufacturers counted in true thousands. The two conventions differ by 2.4 per cent, which was negligible at this scale, but the same error compounds at each step upward and reaches 10 per cent by the teraoctet.
The IEC resolved the ambiguity in 1998 by defining the kibioctet as 1,024 octets and leaving the kilooctet at exactly 1,000. Operating systems have adopted this unevenly: some report file sizes in true kilooctets, others still divide by 1,024 while writing ko, and a few now write Kio correctly.
Where the unit still appears daily is in network protocols and in the sizes of small resources on the web. A web page's stylesheet, an icon, a certificate, a configuration file, a database index page — all of these are measured in kilooctets, and the standard memory page on most processors is 4 kibioctets, close enough to 4 kilooctets for casual conversation but not for arithmetic.
One kilooctet equals 1,000 octets, 8,000 bits, 8 kilobits, or about 0.9766 kibioctets.
The yobibit is a unit of digital information equal to two to the eightieth power bits, which is 1,024 zebibits. Its symbol is Yibit. It is the largest of the binary prefixes defined by the International Electrotechnical Commission, and the binary counterpart of the yottabit.
At this step the two conventions differ by 20.9 per cent. That gap is the culmination of the argument for the binary prefixes: a naming habit that was 2.4 per cent wrong at the kibibit is now a fifth wrong, which no engineering document can tolerate. The IEC series stops here because the decimal series stopped at yotta when it was defined in 1998.
When the metric system gained ronna and quetta in 2022, the binary series was not extended to match. There are no accepted names above yobi, so a quantity of two to the ninetieth bits has no short form and must be written out. This is a gap in the system that will presumably be filled when someone needs it, though at present nothing comes close.
A yobibit is 151,115,727,451,828,646,838,272 octets, or 128 zebioctets. The world's entire stock of data is somewhere in the low hundreds of zettaoctets, which is a fraction of a per cent of a yobioctet. Nothing at this scale has been built, is being built, or is presently planned.
The unit is nevertheless properly defined, and that completeness has a purpose. A measurement system whose rules run out at a certain size forces every future user to invent an extension, and competing extensions are how ambiguity begins. Defining the whole ladder in advance costs nothing and prevents that.
For anyone reading technical documents, the practical lesson of the whole binary series is the lowercase i. Kibit, Mibit, Gibit, Tibit, Pibit, Eibit, Zibit and Yibit are binary; kbit, Mbit, Gbit, Tbit, Pbit, Ebit, Zbit and Ybit are decimal; and the difference between them grows from negligible to a fifth as you climb. A writer who omits the i has left the reader to guess.
One yobibit equals 1,024 zebibits, 151,115,727,451,828,646,838,272 octets, or about 1.209 yottabits.