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Step 3 of 10

The trip

Where is the machine that will answer you?

Make a guess

You ask ChatGPT a question on your phone. Where is the answer computed?

  • On your phone.
  • In the nearest cell tower.
  • In a data center, sometimes very far from you.

Show the answer

The answer: In a data center, sometimes very far from you.

The models behind the big assistants are far too large for a phone. Your question travels to a data center, where the model runs on specialized machines, and the answer comes back the same way.

What happens

  1. Your question leaves your phone as radio waves and reaches the nearest cell tower. On a 4G network, that first hop alone takes Round-trip delay added by the 4G mobile network between your phone and the InternetTypical value for the radio access alone, before the distance covered in the fiberSource: Arcep, La qualité des services mobiles (September 2026)Read at the source, from the organization that produced it..

  2. From the tower, it moves into optical fibers, strands of glass. Lasers send it as flashes of light: count on Round-trip delay through 100 kilometers of optical fiberThe fiber alone; fiber access to the home adds under a millisecond, and network equipment and queues add moreSource: Arcep, La qualité des services mobiles (September 2026)Read at the source, from the organization that produced it..

  3. At the end of the cables is a data center, in your country or on another continent. To cross an ocean, the light follows a cable laid on the seabed, about as thick as a garden hose.

  4. Even from the far side of the world, the round trip takes tenths of a second. What keeps you waiting is the computing: the answer is written token by token, and each one takes a full pass through the model.

  5. The answer's tokens travel the same path in reverse and show up on your screen as they arrive.

Takeaway

The answer isn't computed on your phone. Your question goes out by radio, then travels as light through fiber, sometimes under an ocean, to a data center that may be on another continent.

Go further

The network's electricity

The sources read for this site can't say how much energy the network spends on one question: depending on what you count, the estimates are miles apart. The total is published, though. The world's telecom networks, fixed and mobile, used Electricity used in 2023 by the world's telecommunication networks, fixed and mobile access and coreThe same year, the IEA counts 360 TWh for data centers and 440 TWh for computers, phones and other devicesSource: International Energy Agency, Energy and AI, figure 2.15 (April 2025)Read at the source, from the organization that produced it. in a year, a little less than data centers that same year.

Under the oceans

Between countries, most internet traffic runs through these cables. According to TeleGeography, which keeps track of them, satellites carry only a very small share: a cable moves far more data at far lower cost. For a long time, the cables belonged to groups of telecom operators. Today Google, Meta, Microsoft and Amazon are among the biggest investors in new ones.

Why so far away

A data center needs a lot of electricity, a way to cool its machines, and land. Companies build where they can get all of that, not necessarily near the people asking questions. In fiber, distance costs little time.

A model in your pocket?

Small models fit on a computer, sometimes on a phone. They answer without a network, but they know less and make more mistakes (see "When it gets things wrong").

Sources