1Why Bulbs?
A computer's memory doesn't know letters, words, or pictures. Deep down, it only knows two things: electricity is present, or electricity is absent. That's it. Nothing in between.
We use a light bulb to stand in for one tiny piece of computer memory. A bulb that's lit means 1. A bulb that's dark means 0. Each single bulb is called a bit — short for "binary digit."
One bit isn't very useful on its own — it can only say yes or no. But line up eight bits in a row, and you get 256 different possible patterns. That's exactly enough patterns to represent every letter, number, and symbol on a QWERTY keyboard. Eight bits working together like this is called a byte.
2Flip the Switches, Light the Bulbs
Click a switch to flip its bulb ON or OFF. The number box above each bulb updates instantly to show 1 (on) or 0 (off).
3Build a Message, One Byte at a Time
Every time you click Add to Message, the binary pattern is stacked right above the letter it stands for, and the switches above automatically reset so you're ready for the next one — just like a keyboard sending one keystroke at a time to a computer.
4Now Flip It Around: Keyboard to Binary
You just watched switches build a byte, letter by letter. Now try it the other way: type on your real keyboard, click Show Binary, and watch the bulbs up in section 2 light up on their own, one letter at a time, all the way through your word.
Next up: we take this exact byte and follow it down through the OSI Protocol Stack — from Physical bits, to Data Link frames, all the way to Application data on the receiving computer.