| Exabits per second (Ebit/s) | Kilobits per second (kbit/s) |
|---|---|
| 1 Exabit per second | 1 × 1015 kbit/s |
| 2 Exabits per second | 2 × 1015 kbit/s |
| 3 Exabits per second | 3 × 1015 kbit/s |
| 4 Exabits per second | 4 × 1015 kbit/s |
| 5 Exabits per second | 5 × 1015 kbit/s |
| 10 Exabits per second | 1 × 1016 kbit/s |
| 20 Exabits per second | 2 × 1016 kbit/s |
| 25 Exabits per second | 2.5 × 1016 kbit/s |
| 50 Exabits per second | 5 × 1016 kbit/s |
| 100 Exabits per second | 1 × 1017 kbit/s |
| Reference | Exabits per second (Ebit/s) | Kilobits per second (kbit/s) |
|---|---|---|
| A dial-up modem | 5.6 × 10-14 Ebit/s | 56 kbit/s |
| Typical home broadband | 1 × 10-10 Ebit/s | 100000 kbit/s |
| Gigabit Ethernet | 0.000000001 Ebit/s | 1000000 kbit/s |
| Streaming a 4K film | 2.5 × 10-11 Ebit/s | 25000 kbit/s |
The exabit per second is a unit of data transfer rate equal to a thousand petabits per second. Its symbol is Ebit/s. No link, no cable and no exchange point runs at this rate; the unit describes the internet as a whole, or a large part of it, at a single instant.
Global internet traffic can be expressed this way. Worldwide traffic of several hundred exaoctets a month works out to roughly one exabit per second on average, and peak hours run higher. That figure is the sum of every packet moving on every network on the planet, and it is the only quantity anyone routinely describes at this scale.
An exabit per second is 125 petaoctets per second. Nothing generates data at that rate in one place; the number is an aggregate of billions of separate flows, most of them tiny. A single video stream is a few megabits per second, so an exabit per second is on the order of a hundred million such streams running at once.
The composition of that traffic is dominated by video. Streaming services account for the largest share, followed by social platforms, software updates and cloud synchronisation. Ordinary web browsing and messaging, which people think of as the internet, are a small fraction of the total by volume even though they occupy most of the attention.
The unit also appears in projections of aggregate capacity. The total installed capacity of all submarine cables, if every wavelength on every fibre pair were lit and used simultaneously, is in the exabit-per-second range. Actual utilisation is far below that, because capacity is built ahead of demand and because routes must carry each other's traffic when a cable fails.
The prefix exa is a thousand to the sixth power. It was adopted in 1975, when nobody expected it to describe anything but astronomical quantities, and it now describes the working throughput of a communications system built by human beings. The interval between definition and everyday use was about forty years.
One exabit per second equals 1,000 petabits per second, 125 petaoctets per second, or about 0.8674 exbibits per second.
The kilobit per second is a unit of data transfer rate equal to one thousand bits per second. Its symbol is kbit/s, often written kbps. It was the unit of the dial-up era, and it survives today as the unit in which audio and speech encoding rates are quoted.
The dial-up sequence is worth recalling because each number marks a technical generation. Modems ran at 300 bits per second in the late 1970s, then 1,200, 2,400, 9,600, 14,400, 28,800, 33,600 and finally 56 kilobits per second at the end of the 1990s. That last figure was the ceiling of an ordinary telephone line, set by the eight-kilohertz sampling of the digital telephone network rather than by the modem.
Audio encoding is where the unit now lives. Telephone-quality speech runs at 8 to 64 kilobits per second depending on the codec, with modern low-rate codecs producing intelligible speech at 8 and high-quality voice calls at 24 to 32. Music at 128 kilobits per second was the early standard of portable players, 192 and 256 are common, and 320 is the practical ceiling of the older lossy formats.
Those numbers reward a moment of arithmetic. Music at 128 kilobits per second is 16 kilooctets per second, so a four-minute track is about 3.8 megaoctets. Uncompressed compact-disc audio runs at 1,411 kilobits per second, so the compressed file is about a tenth the size of the original, which is the whole point of the format.
Video subtitle streams, control channels and telemetry links also work in kilobits per second. So does much of the machine-to-machine traffic that fills modern networks: a sensor reporting a reading every few seconds needs a fraction of a kilobit per second, and the protocols designed for such devices are built around keeping the radio switched off most of the time.
The unit's lower-case k marks the decimal kilo, one thousand exactly. In transmission this has never been ambiguous, because network rates have always been counted in true thousands; the binary confusion that afflicts storage units does not arise here, and a kilobit per second means the same thing in every document.
One kilobit per second equals 1,000 bits per second, 125 octets per second, or about 0.9766 kibibits per second.