You tap the screen

The video is not in your phone

In a room in Busan, Korea, you tap a video on your phone. But that video is not inside your phone. It is stored on a computer across the ocean, in the United States. So first, your phone sends a short message, a request, that says "please send this video."

Why?There are far too many videos, and they are far too big, to keep them all on a phone. So the phone fetches a video each time you watch it, a bit like ordering a delivery. The request carries two addresses, like a parcel: where it is going, and where it came from (your phone).

Learn moreThe number at the top of the screen is a clock. "ms" means a thousandth of a second. One blink of an eye takes about 100 to 400 ms. This story follows a video stored on its original computer in the US. In the last scenes, we will see that popular videos work a little differently. The address is a number called an "IP address."

Time

0 ms → 0.4 ms

Simplified route · light in glass at about 200,000 km per second