THE ARITHMETIC AND LOGIC UNIT

The arithmetic and logic unit performs all computations (addition, subtraction, multiplication, and division) and all logic operations (comparisons). The results are placed in a register called the accumulator. Examples of computations include the payroll deduction for social security, the day-end inventory, and the balance on a bank statement. A logic operation compares two pieces of data, either alphabetic or numeric. Based on the result of the comparison, the program "branches" to one of several alternative sets of program instructions. For example, in an inventory system each item in stock is compared to a reorder point at the end of each day. If the inventory level falls below the reorder point, a sequence of program instructions is executed that produces a purchase order