ALU

The arithmetic logic unit (ALU) is a digital circuit that calculates an arithmetic operation (addition, subtraction, etc.) and logic operations (Exclusive or, AND, etc.) between two numbers. The ALU is a basic building block of the central processing unit of a computer. Many types of electronic circuits require performing some type of arithmetic operation, so even the circuit within a digital watch will have a tiny ALU that keeps adding 1 to the current time, and keeps checking if it should beep the timer, etc...

By far, the most complex electronic circuits are those that are built within the chip of modern microprocessors like the Pentium. Therefore, these processors have inside them a powerful and very complex ALU. In fact, recent microprocessor (or mainframe) may have multiple cores, each core with multiple execution units, each with multiple ALUs.