| Kilooctets (ko) | Zebibits (Zibit) |
|---|---|
| 1 Kilooctet | 6.77626357803 × 10-18 Zibit |
| 2 Kilooctets | 1.35525271561 × 10-17 Zibit |
| 3 Kilooctets | 2.03287907341 × 10-17 Zibit |
| 4 Kilooctets | 2.71050543121 × 10-17 Zibit |
| 5 Kilooctets | 3.38813178902 × 10-17 Zibit |
| 10 Kilooctets | 6.77626357803 × 10-17 Zibit |
| 20 Kilooctets | 1.35525271561 × 10-16 Zibit |
| 25 Kilooctets | 1.69406589451 × 10-16 Zibit |
| 50 Kilooctets | 3.38813178902 × 10-16 Zibit |
| 100 Kilooctets | 6.77626357803 × 10-16 Zibit |
| Reference | Kilooctets (ko) | Zebibits (Zibit) |
|---|---|---|
| A plain text message (160 characters) | 0.16 ko | 1.0842 × 10-18 Zibit |
| A three-minute MP3 | 3000 ko | 2.03288 × 10-14 Zibit |
| A smartphone photo | 4000 ko | 2.71051 × 10-14 Zibit |
| A high-definition film | 4000000 ko | 2.71051 × 10-11 Zibit |
| A dual-layer Blu-ray disc | 50000000 ko | 3.38813 × 10-10 Zibit |
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 zebibit is a unit of digital information equal to two to the seventieth power bits, which is 1,024 exbibits. Its symbol is Zibit. It is the binary counterpart of the zettabit, and the two now differ by 18.1 per cent — nearly a fifth.
That divergence is the reason the binary prefixes were needed at all. At the kibibit the two conventions differed by 2.4 per cent, a rounding error. Here the difference is large enough that a document using the wrong one is simply reporting a different quantity, and no amount of context can repair the ambiguity after the fact.
A zebibit is 147,573,952,589,676,412,928 octets, or 128 exbioctets. Nothing of this size exists. The total data held by humanity is somewhere in the low hundreds of zettaoctets, which is under a zebioctet, so the world's entire information stock does not yet reach one unit at this step of the binary ladder.
The unit exists because the IEC series was defined completely rather than as far as anyone then needed. That is the same principle the metric system follows: every prefix applies to every unit, whether or not the combination has yet been used. A system with holes in it requires a table of exceptions, and a system without holes requires only the rule.
Where the zebibit could genuinely appear is in address space arithmetic. Two to the seventieth is not a natural pointer width, but multiples and fractions of powers of two run through every discussion of addressing, and a scheme that reserved seventy bits for something would naturally be described in these terms. Such schemes are proposed occasionally and none has yet been needed.
Reading the symbol is the practical skill. Zibit is binary, Zbit is decimal, and at eighteen per cent apart the two are not interchangeable in any document where the number matters. Where a source writes ZB with no explanation, there is no way to know which was meant, and the honest response is to treat the figure as uncertain to a fifth.
One zebibit equals 1,024 exbibits, 147,573,952,589,676,412,928 octets, or about 1.181 zettabits.