What is latency?
In one sentence: How long a message takes to get somewhere and back. Measured in milliseconds.
A little more
Latency is the waiting time before an answer arrives. It's mostly set by distance: light in glass fibre covers about 200 km every millisecond, so London to New York and back takes at least 55 ms however fast the computers are.
Speed (bandwidth) is how much data can flow at once; latency is how long the first bit takes. Video calls and games care most about latency; downloads care about bandwidth.
It's a bit like… Shouting across a valley and waiting for the echo: a bigger voice doesn't make the echo come back sooner.
See it in action
- BonusWhy does every speed test give a different answer?A speed test is a water-balloon race: fill a balloon from the internet tap for ten seconds and divide the water by the time.9 min · interactive
- 1What happens when you open a web page?Follow one click from your keyboard to a server and back: DNS, the padlock handshake, HTTP, tunnels and painting the page.6 min · interactive
- 6How does a message cross the world in a blink?Race an undersea cable against satellites between any two cities, see why glass threads on the sea floor carry almost all the world's data, and chop a message into packets that arrive in a jumble..7 min · interactive
- 14How can lots of people play the same game together?Share a pretend park with friends in other houses: every move is a message to a shared world on a server.7 min · interactive
- BonusWhy does the game lag when someone starts a download?Your internet line is a shop with one checkout and a download is a shopper with endless trolleys.9 min · interactive
- BonusHow does a game controller talk to a console?Your controller fires tiny paper darts at the console hundreds of times a second, each one a snapshot of every button and stick.8 min · interactive
Do it for real
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