Arithmetic and Logic Unit

AIRTHEMATIC AND LOGIC (ALU):

DEFINITION:


In digital electronics, an arithmetic logic unit(An arithmetic logic unit (ALU) represents the fundamental building block of the central processing unit of a computer. An ALU is a digital circuit used to perform arithmetic and logic operations.) is a digital circuit that performs integer arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes  Short for Arithmetic Logic Unit, ALUIn some computer processors, the ALU is divided into an AU and LU. The AU performs the arithmetic operations and the LU performs the logical operations.




An arithmetic logic unit (ALU) is a digital circuit used to perform arithmetic and logic operations. It represents the fundamental building block of the central processing unit (CPU) of a computer. Modern CPUs contain very powerful and complex ALUs. In addition to ALUs, modern CPUs contain acontrol unit (CU). Most of the operations of a CPU are performed by one or more ALUs, which load data from input registers. A register is a small amount of storage available as part of a CPU. The control unit tells the ALU what operation to perform on that data and the ALU stores the result in an output register. The control unit moves the data between these registers, the ALU and memory.How An ALU WorksAn ALU performs basic arithmetic and logic operations. Examples of arithmetic operations are addition, subtraction, multiplication, and division. Examples of logic operations are comparisons of values such as NOT, AND, and OR.All information in a computer is stored and manipulated in the form of binary numbers, i.e. 0 and 1.Transistor switches are used to manipulate binary numbers, since there are only two possible states of a switch: open or closed. An open transistor, through which there is no current, represents a 0. A closed transistor, through which there is a current, represents a 1. Operations can be accomplished by connecting multiple transistors. One transistor can be used to control a second one, in effect turning the transistor switch on or off depending on the state of the second transistor. This is referred to as a gate, because the arrangement can be used to allow or stop a current.The simplest type of operation is a NOT gate. This uses only a single transistor. It uses a single input and produces a single output, which is always the opposite of the input. The figure below shows the logic of the NOT gate.Other gates consist of multiple transistors and use two inputs. The OR gate results in a 1 if either the first or the second input is a 1. The OR gate only results in a 0 if both inputs are 0. The figure below shows the logic of the OR gate. 

The AND gate results in a 1 only if both the first and second input are 1s. The figure below shows the logic of the AND gate.
The XOR gate results in a 0 if both the inputs are 0 or if both are 1. Otherwise, the result is a 1. The figure below shows the logic of the XOR gate.

The various gates sound a little abstract, but remember that a computer only processes binary data. When you follow the binary logic of these operations, you are starting to think like a computer.