| Kibioctets (Kio) | Megaoctets (Mo) |
|---|---|
| 1 Kibioctet | 0.001024 Mo |
| 2 Kibioctets | 0.002048 Mo |
| 3 Kibioctets | 0.003072 Mo |
| 4 Kibioctets | 0.004096 Mo |
| 5 Kibioctets | 0.00512 Mo |
| 10 Kibioctets | 0.01024 Mo |
| 20 Kibioctets | 0.02048 Mo |
| 25 Kibioctets | 0.0256 Mo |
| 50 Kibioctets | 0.0512 Mo |
| 100 Kibioctets | 0.1024 Mo |
| Reference | Kibioctets (Kio) | Megaoctets (Mo) |
|---|---|---|
| A plain text message (160 characters) | 0.15625 Kio | 0.00016 Mo |
| A three-minute MP3 | 2929.69 Kio | 3 Mo |
| A smartphone photo | 3906.25 Kio | 4 Mo |
| A high-definition film | 3906250 Kio | 4000 Mo |
| A dual-layer Blu-ray disc | 48828125 Kio | 50000 Mo |
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.
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.