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Binary numbers
Every number can be written using only 0s and 1s. That's how every computer does arithmetic.
Binary — count in 0s and 1s
Each switch is twice the one to its right. Click to flip.
0
00000000
Each bit is worth twice the one to its right: 1, 2, 4, 8, 16, 32, 64, 128. Add up the switches that are on.
Why two?
Computer chips can detect "on" or "off" reliably, but anything in between is noisy. Two states is the most resilient choice — and that's why every digital device on Earth counts in binary.
Reading binary
Each bit doubles. So
1011 is 8 + 0 + 2 + 1 = 11. Read right-to-left, the place values are 1, 2, 4, 8, 16, 32, 64, 128…