| Kibioctets (Kio) | Pebioctets (Pio) |
|---|---|
| 1 Kibioctet | 9.09494701773 × 10-13 Pio |
| 2 Kibioctets | 1.81898940355 × 10-12 Pio |
| 3 Kibioctets | 2.72848410532 × 10-12 Pio |
| 4 Kibioctets | 3.63797880709 × 10-12 Pio |
| 5 Kibioctets | 4.54747350886 × 10-12 Pio |
| 10 Kibioctets | 9.09494701773 × 10-12 Pio |
| 20 Kibioctets | 1.81898940355 × 10-11 Pio |
| 25 Kibioctets | 2.27373675443 × 10-11 Pio |
| 50 Kibioctets | 4.54747350886 × 10-11 Pio |
| 100 Kibioctets | 9.09494701773 × 10-11 Pio |
| Reference | Kibioctets (Kio) | Pebioctets (Pio) |
|---|---|---|
| A plain text message (160 characters) | 0.15625 Kio | 1.42109 × 10-13 Pio |
| A three-minute MP3 | 2929.69 Kio | 0.00000000266454 Pio |
| A smartphone photo | 3906.25 Kio | 0.00000000355271 Pio |
| A high-definition film | 3906250 Kio | 0.00000355271 Pio |
| A dual-layer Blu-ray disc | 48828125 Kio | 0.0000444089 Pio |
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 pebioctet is a unit of digital information equal to 1,125,899,906,842,624 octets, which is 1,024 tebioctets. Its symbol is Pio. It is the binary counterpart of the petaoctet, and the two now differ by 12.6 per cent.
This is the unit in which filesystem limits are written. Several widely deployed filesystems have maximum file or volume sizes that are exact powers of two, and those limits fall in this range: sixteen tebioctets for one, a pebioctet for another, eight pebioctets for a third. The numbers are not choices made by anyone; they follow from how many bits the filesystem uses to number its blocks.
Large scientific and commercial storage systems are also sized here. A research computing centre may run a filesystem of several pebioctets across thousands of drives, and the tools that manage it report in pebioctets because the underlying allocation is binary throughout. Converting those figures to decimal units for a report introduces an error of an eighth for no benefit.
A pebioctet is roughly a thousand large consumer hard drives, or the complete video output of a broadcaster over many years. It is also close to the size of the largest single scientific archives, though those are typically stated in petaoctets by press offices and in pebioctets by the engineers who run them, which produces two different numbers for the same building.
Distinguishing the two is not pedantry at this level. A twelve per cent difference on a purchase of many pebioctets is a large sum of money, and a capacity plan built on the wrong unit will be wrong by more than the margin most plans allow. This is precisely the situation the IEC prefixes were introduced to prevent.
The symbol Pio is used in filesystem documentation, in storage system manuals and in standards. Where a source writes PB without saying which it means, the difference is an eighth, and the honest thing for a reader to do is treat the figure as approximate rather than assume one convention or the other.
One pebioctet equals 1,024 tebioctets, 1,125,899,906,842,624 octets, 8 pebibits, or about 1.126 petaoctets.