How a Webpage Reaches You

Half a second, a very long way

Tap a link. The page appears. It feels like opening a drawer.

It isn't. In that half second your device had to work out where the page lives, get a message to a computer that might be four thousand miles away, and get an answer back — and it did all of that through machines that have never heard of you and don't keep track of you.

There are about five separate systems doing five separate jobs in there. Here they are, in the order they happen.

Step one: names are for people

Websites have names because humans are bad at numbers. Computers on the internet don't have names — they have IP addresses, which look like `93.184.215.14`, or in the newer style, a much longer string of letters and digits.

So before anything else can happen, the name you typed has to be turned into a number. Your device asks a name server: what is the address for this name? That system is called DNS, the Domain Name System, and you can think of it as the world's phone book — except no single copy of it exists anywhere. It's split across millions of machines, each responsible for a slice, each able to say "not me, ask that one over there."

One tap, counted in milliseconds

Here is a typical page load on a decent connection, one step at a time. The right column is the clock, running from the moment your finger lifts. A millisecond is a thousandth of a second — so watch how little of this is actually the page itself.

Nothing travels in one piece

Here's the part that surprises most people. Your request doesn't travel as a single object, and neither does the page coming back. Both get chopped into small chunks called packets, and each packet is sent off on its own.

Each packet carries the address it's going to, the address it came from, and a number saying which piece of the whole it is. That last part is what makes the trick work: the pieces can arrive out of order, take different routes, or go missing entirely, and the machine at the far end can still put the original back together — and ask for any missing piece again.

Nobody is planning the journey

Between you and the server sit a chain of machines called routers, usually ten to twenty of them. And here is the genuinely strange bit: not one of them knows the whole route.

A router looks at a packet's destination and asks itself a single question — which of my neighbours is closer to that? — then hands it over and forgets about it. That's the whole job. The full path emerges from a dozen machines each making one small local decision, which is exactly why the internet survives a cable being cut: the packets simply start getting handed a different way, and nothing had to be told to reroute.

It also means two packets from the same page can genuinely take different paths and still both arrive.

Sort what the internet actually is

Some of these you have just been taught. Some are the versions people repeat because they sound right. Sort each one and read what it says.

The cables under the ocean

If your request crosses an ocean, it goes through a cable on the seabed. There are more than 600 of these, stretching well over a million kilometres in total, and they carry over 99% of all traffic between continents. Some are about as thick as a garden hose. Inside, glass fibres thinner than a hair carry your page as pulses of light.

This is why a ship's anchor in the wrong place can slow down a whole country's internet, and it is also why nobody with any sense builds only one cable to anywhere.

There is a speed limit, and it is not negotiable

Light in a glass fibre travels at roughly 200,000 kilometres per second — about two-thirds of its speed in empty space, because glass slows it down.

So do the arithmetic for New York to London, which is about 5,570 kilometres of cable. One way takes around 28 thousandths of a second. There and back: about 56 milliseconds, and that is the absolute floor. Not the speed of today's cables — the speed of light itself, in glass. No amount of money makes it quicker.

Real traffic on that route usually measures 70 to 80 milliseconds, and the gap between 56 and 75 is the routers, the switching gear, and the fact that no cable is drawn perfectly straight.

That unbeatable floor is why big companies stopped trying to send you things faster and started keeping copies of themselves nearer to you instead. The video you streamed last night almost certainly came from a building in your own country, not from wherever the company happens to live.

What to keep