| Petabits (Pbit) | Exbibits (Eibit) |
|---|---|
| 1 Petabit | 0.000867361737988 Eibit |
| 2 Petabits | 0.00173472347598 Eibit |
| 3 Petabits | 0.00260208521397 Eibit |
| 4 Petabits | 0.00346944695195 Eibit |
| 5 Petabits | 0.00433680868994 Eibit |
| 10 Petabits | 0.00867361737988 Eibit |
| 20 Petabits | 0.0173472347598 Eibit |
| 25 Petabits | 0.0216840434497 Eibit |
| 50 Petabits | 0.0433680868994 Eibit |
| 100 Petabits | 0.0867361737988 Eibit |
| Reference | Petabits (Pbit) | Exbibits (Eibit) |
|---|---|---|
| A plain text message (160 characters) | 1.28 × 10-12 Pbit | 1.11022 × 10-15 Eibit |
| A three-minute MP3 | 0.000000024 Pbit | 2.08167 × 10-11 Eibit |
| A smartphone photo | 0.000000032 Pbit | 2.77556 × 10-11 Eibit |
| A high-definition film | 0.000032 Pbit | 0.0000000277556 Eibit |
| A dual-layer Blu-ray disc | 0.0004 Pbit | 0.000000346945 Eibit |
The petabit is a unit of digital information equal to a thousand terabits, or a million billion bits. Its symbol is Pbit. It sits at the boundary between quantities that are routinely deployed and quantities that still belong to research laboratories and to totals aggregated across whole networks.
A petabit is 125 teraoctets. That is the storage of roughly a hundred and twenty-five large consumer hard drives, or in more everyday terms about thirty thousand hours of high-definition video — three and a half years of continuous viewing. No single device holds a petabit; the figure describes systems rather than objects.
The most striking use of the unit is in optical transmission records. Research groups in Japan, the Netherlands and elsewhere have carried more than a petabit per second down a single strand of fibre, achieved by combining multi-core fibre — several light-guiding paths inside one cladding — with hundreds of separate wavelengths and advanced modulation. Those results run over tens of kilometres in the laboratory, not the thousands of kilometres a working sea cable must cross.
At the network level the petabit describes aggregate capacity. The total interconnect capacity of a large data centre, the combined capacity of all cables landing on a continent, and the peak throughput of the largest content networks are all quoted in petabits per second. These are sums over many links rather than the rating of any one of them.
Storage systems reach petabit scale too, though they are always labelled in octets. A large scientific archive holding a hundred petaoctets is holding eight hundred petabits, and facilities of that size exist for genomics, particle physics and astronomical survey data. The particle detectors at CERN discard the vast majority of what they see precisely because keeping it would exceed even these capacities.
The prefix peta comes from the Greek for five, because a petabit is a thousand raised to the fifth power in bits. That naming pattern continues upward with exa for six and zetta for seven, so the ladder above the petabit is regular and easy to extend.
One petabit equals 1,000,000,000,000,000 bits, 1,000 terabits, 125 teraoctets, or about 0.8882 pebibits.
The exbibit is a unit of digital information equal to two to the sixtieth power bits, which is 1,024 pebibits. Its symbol is Eibit. It is the binary counterpart of the exabit, and the two now differ by 15.3 per cent.
Two to the sixtieth is a number with a particular importance in computing, because sixty is close to the sixty-four bits of a modern processor address. A 64-bit machine can address sixteen exbioctets of memory, and that figure — 16 EiB — is the theoretical ceiling of the entire architecture. It appears in processor manuals, in operating system documentation and in the specification of every 64-bit filesystem.
No machine comes close to using that range. Current processors implement only forty-eight or fifty-seven of those sixty-four address bits, because wiring the full width would cost silicon for an address space nobody can fill. The unused bits are reserved, and widening the implementation is a straightforward matter whenever memory sizes make it worthwhile, which is the point of having chosen sixty-four in the first place.
An exbibit is 144,115,188,075,855,872 octets, or 128 pebioctets. That is more storage than any single organisation holds, and comparable to the combined annual output of a large part of the storage industry. As with all the larger binary units, it describes limits and capacities in specifications rather than anything that has been built.
The unit is also where filesystem designers set their maximum sizes. Filesystems built around 64-bit block pointers naturally have limits at exact powers of two, and several widely deployed ones specify maximum volume sizes in exbioctets. Those numbers are not aspirations; they are the arithmetic consequence of the pointer width, and they will hold until the architecture changes.
Reading the symbol correctly matters here. Eibit is the exbibit; Ebit is the exabit; EB and EiB are the octet forms of each. In a document where a fifteen per cent difference is significant — and at this scale it always is — the presence or absence of the lowercase i carries the entire meaning.
One exbibit equals 1,024 pebibits, 144,115,188,075,855,872 octets, or about 1.153 exabits.