# Specialty Circuits

All circuits within the computer are made from a combination of basic logic gates. Circuits can be designed to perform addition, subtracting (using complementary addition) and comparisons to determine equality. As the number of inputs increases, the circuits become more complex.

Logic circuits may be combinational or sequential. Combinational circuits produce instant output, determined by the combination of logic gates. Sequential circuits contain memory cells as well as logic gate. The state of the memory cells is determined by previous inputs. Memory cells are implemented using flip-flops.

Digital computers perform arithmetic operations as well as boolean operation. The most basic arithmetic operations is the addition of two binary digits. The addition of two binary digits has four possible countcomes: 0 + 0 = 0;0 + 1: 1 + 0 = 1 and 1 + 1 = 10. When two ones are added, the result consists of two digits. The higher significant bit (1) is called a carry.