Adding Machines

Half adders and full adders

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Half adder: sum = A XOR B, carry = A AND B.
• A full adder also takes a carry in. Chained together, they add numbers of any length.
• Ripple carries are slow, so fast chips predict carries in advance.

Steps

1. Adding single bits
2. A half adder
3. Full adders in a chain
4. Add in binary
5. Room for the carry
6. Why it ripples
7. Watch the carry ripple