| Bits (bit) | Gibioctets (Gio) |
|---|---|
| 1 Bit | 1.16415321827 × 10-10 Gio |
| 2 Bits | 2.32830643654 × 10-10 Gio |
| 3 Bits | 3.49245965481 × 10-10 Gio |
| 4 Bits | 4.65661287308 × 10-10 Gio |
| 5 Bits | 5.82076609135 × 10-10 Gio |
| 10 Bits | 0.00000000116415321827 Gio |
| 20 Bits | 0.00000000232830643654 Gio |
| 25 Bits | 0.00000000291038304567 Gio |
| 50 Bits | 0.00000000582076609135 Gio |
| 100 Bits | 0.0000000116415321827 Gio |
| Reference | Bits (bit) | Gibioctets (Gio) |
|---|---|---|
| A plain text message (160 characters) | 1280 bit | 0.000000149012 Gio |
| A three-minute MP3 | 24000000 bit | 0.00279397 Gio |
| A smartphone photo | 32000000 bit | 0.00372529 Gio |
| A high-definition film | 3.2 × 1010 bit | 3.72529 Gio |
| A dual-layer Blu-ray disc | 4 × 1011 bit | 46.5661 Gio |
The bit is the fundamental unit of information. Its symbol is bit, and its name is a contraction of binary digit, coined by the statistician John Tukey and put into print by Claude Shannon in his 1948 paper A Mathematical Theory of Communication, the work that founded information theory.
A bit is the amount of information carried by a single choice between two equally likely possibilities. A coin landing heads or tails, a switch open or closed, a voltage high or low: each of those settles one bit. That definition is what makes the bit a unit rather than a mere convention of notation. It measures how much uncertainty an answer removes, and it does so in a way that is independent of what the question was about.
Shannon's insight was that this could be counted. A message drawn from an alphabet of thirty-two equally likely symbols carries five bits per symbol, because thirty-two is two to the fifth. If the symbols are not equally likely — as letters in English are not — the average drops, and that gap between the naive count and the true average is exactly what compression exploits. A well-compressed file is one from which the redundant bits have been removed.
In hardware the bit is a physical state: a charge trapped on a floating gate in flash memory, the direction of magnetisation of a domain on a hard disc platter, a pit or land on an optical disc, a pulse of light present or absent in a fibre. All of these encode the same abstract quantity, which is why data can move between them without loss.
Bits are almost never counted singly in storage. They are grouped into octets of eight, and storage capacity is quoted in octets or their multiples. Transmission is different: network and interface speeds are quoted in bits per second, so a connection described as 100 megabits per second delivers about 12.5 megaoctets per second. Confusing the two is the commonest arithmetic error in the whole field.
Where single bits do get counted is in specifications of precision and range. A colour channel with 8 bits holds 256 levels; one with 10 bits holds 1,024. Audio at 16 bits per sample has about 96 decibels of dynamic range, and at 24 bits about 144. A 64-bit address can name about 18 quintillion locations. In every case, each added bit doubles what can be distinguished.
One bit equals 0.125 octets, 0.001 kilobits, or about 0.0009766 kibibits.
The gibioctet is a unit of digital information equal to 1,073,741,824 octets, which is 1,024 mebioctets. Its symbol is Gio. It is the binary counterpart of the gigaoctet, and the 7.4 per cent difference between them is the single most common cause of confusion about data units.
This is the unit in which computer memory is actually sold, whatever the packaging says. A module labelled 8 GB holds 8 gibioctets, which is 8.59 gigaoctets. It could not hold anything else: memory addressing is binary, and a module with a decimal capacity would leave part of its address range unpopulated. The label is a convenient shorthand rather than a measurement.
Storage, by contrast, is genuinely decimal. A drive sold as 500 gigaoctets holds five hundred thousand million octets, and the operating system divides that by 1,024 three times and reports 465.7 gibioctets. The two figures describe the same hardware. Neither party is being dishonest; they are simply counting in different bases, and the labelling convention differs by industry.
Cloud computing has made the distinction visible in contracts. Virtual machine sizes, container memory limits and the parameters that control how much memory a program may use are all specified in gibioctets, because they map onto real memory pages. A limit of 4 GB set in a decimal-minded tool and 4 GiB set in a binary one differ by nearly three hundred megaoctets, which is enough to change whether a program runs.
For everyday scale, a gibioctet holds about a thousand books as plain text, a few hundred photographs, or twenty minutes of high-definition video. It is roughly what a modern web browser occupies in memory with a dozen pages open, which is a fair illustration of how the standard for what counts as a small amount has moved.
The correct symbol is Gio, and it appears in system tools, in virtualisation documentation and in standards. Where a document writes GB for memory, the safe reading is gibioctets; where it writes GB for a disc or a network, the safe reading is gigaoctets. The habit of checking which is meant costs a second and prevents a seven per cent error.
One gibioctet equals 1,073,741,824 octets, 1,024 mebioctets, 8 gibibits, or about 1.074 gigaoctets.