| Terabits (Tbit) | Pebibits (Pibit) |
|---|---|
| 1 Terabit | 0.0008881784197 Pibit |
| 2 Terabits | 0.0017763568394 Pibit |
| 3 Terabits | 0.0026645352591 Pibit |
| 4 Terabits | 0.0035527136788 Pibit |
| 5 Terabits | 0.0044408920985 Pibit |
| 10 Terabits | 0.008881784197 Pibit |
| 20 Terabits | 0.017763568394 Pibit |
| 25 Terabits | 0.0222044604925 Pibit |
| 50 Terabits | 0.044408920985 Pibit |
| 100 Terabits | 0.08881784197 Pibit |
| Reference | Terabits (Tbit) | Pebibits (Pibit) |
|---|---|---|
| A plain text message (160 characters) | 0.00000000128 Tbit | 1.13687 × 10-12 Pibit |
| A three-minute MP3 | 0.000024 Tbit | 0.0000000213163 Pibit |
| A smartphone photo | 0.000032 Tbit | 0.0000000284217 Pibit |
| A high-definition film | 0.032 Tbit | 0.0000284217 Pibit |
| A dual-layer Blu-ray disc | 0.4 Tbit | 0.000355271 Pibit |
The terabit is a unit of digital information equal to one million million bits, a thousand gigabits. Its symbol is Tbit. It is the scale at which the internet's own infrastructure is measured — not the connection into a house, but the links between cities and across oceans.
A terabit is 125 gigaoctets. Put another way, one terabit is roughly the amount of data in a hundred and twenty-five hours of high-definition video, or the contents of a large laptop's disc. A single terabit-per-second link therefore moves the equivalent of that laptop every second, continuously.
Submarine cables are where these numbers live. A modern transoceanic cable carries several hundred terabits per second across a handful of fibre pairs, using wavelength division multiplexing to run dozens of separate light channels down the same glass strand at once. The cables laid across the Atlantic in the 2020s reach into the hundreds of terabits, where the first transatlantic telephone cable of 1956 carried thirty-six voice calls.
Internet exchange points, where networks meet and hand traffic to one another, publish their throughput in terabits per second. The largest in Europe and Asia peak in the tens of terabits, and those figures are among the most reliable public measurements of how much the internet is actually being used at a given moment.
Laboratory records go far higher. Research teams have pushed single optical fibres past a petabit per second by using multi-core fibre and hundreds of wavelengths simultaneously, though such experiments run over short distances under controlled conditions. The gap between what is demonstrated in a laboratory and what is deployed in the sea is usually about a decade.
For storage the terabit is used mainly in the semiconductor industry, where the density of a memory die is quoted in terabits per square centimetre or per package. Consumer products are labelled in octets instead — a terabit is 125 gigaoctets, so a chip described as 8 terabits appears on the shelf as a one-teraoctet drive.
One terabit equals 1,000,000,000,000 bits, 1,000 gigabits, 125 gigaoctets, or about 0.9095 tebibits.
The pebibit is a unit of digital information equal to 1,125,899,906,842,624 bits, which is 1,024 tebibits or two to the fiftieth power. Its symbol is Pibit. It is the binary counterpart of the petabit, and the gap between them has widened to 12.6 per cent.
That widening is worth watching, because it is the whole argument for the IEC prefixes in one number. Each step up the ladder multiplies the discrepancy by 1.024, so what began as a harmless 2.4 per cent at the kibibit is an eighth of the quantity here and a fifth at the yobibit. A convention that was reasonable for small numbers becomes indefensible for large ones.
A pebibit is 140,737,488,355,328 octets, or 128 tebioctets. Storage of this size exists in supercomputer memory systems, in the fastest scientific data buffers and in the aggregate memory of very large clusters. The largest machines on the list of the world's fastest computers have main memory measured in pebioctets, and the ability to hold an entire simulation in memory rather than on disc is what makes certain calculations feasible at all.
Because these systems are addressed in binary, the binary unit is the correct one and the decimal figure would be an approximation. A cluster with a pebibit of memory does not have a petabit; it has 12.6 per cent more, and a scheduler that allocated on the decimal figure would leave that much unused.
The unit also appears in filesystem limits. Several widely used filesystems have maximum volume or file sizes expressed as exact powers of two, and where those limits fall in this range they are naturally written in pebibytes or pebioctets. Documentation that converts them to decimal units loses the property that made them memorable.
In everyday computing the pebibit is never encountered. It belongs to specifications, to system architecture and to the design of the largest machines, and a converter needs it for exactly those documents. Anywhere the underlying quantity is a power of two, this is the unit that says so without rounding.
One pebibit equals 1,024 tebibits, 140,737,488,355,328 octets, or about 1.126 petabits.