Computers carry out addition using circuits called binary adders. As computers do everything in 0s and 1s, binary adders must be combined to add numbers of several digits. They do this by having two outputs, sum and carry. The sum is the result of adding the inputs together. If both are 1, the output should be 2, which in binary is 10. The carry output becomes 1 to move the digit representing 2 into the next adder along.