Page 15 - Computer Science Class 11 Without Functions
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Several registers are also equipped with circuitry for performing elementary operations like addition and subtraction.
               However, as the registers are much more expensive than the main memory, the CPU has only a limited number of
               them.
              Arithmetic Logic Unit (ALU): The Arithmetic Logic Unit (ALU) of the CPU performs all arithmetic (+,-,*,/) and logical
               (>,<,>=,<=,<>)  operations.  While  the  result  of  an  arithmetic  operation  is  a  numeric  value,  the  result  of  a  logical
               operation (such as 7<8) is either True or False. The values True and False are called Boolean values in honour
               of George Boole, who developed an algebra (again named, Boolean algebra, in his honour) that constitutes the basis
               of  all  computer  computations.  The  data  for  executing  an  instruction  may  already  be  available  in  the  registers  or
               fetched in the ALU registers from the computer's memory. The result of a computation is often stored in the computer's
               memory.

              Control Unit (CU): The Control Unit (CU) controls the execution of instructions and the flow of data amongst the
               components of a computer, i.e., from input devices to memory, memory to ALU and vice versa, and from memory
               to output devices. It sends instructions in the form of control signals to ALU to perform the required arithmetic and/
               or logical operations.



                                                        Central Processing
                                                              Unit

                                                           Cache
                                          Main            Memory
                                         Memory                              Input/Output
                                                                                Devices
                                                            ALU

                                        Backing or
                                         Auxiliary                           Key
                                         Storage         Control Unit            Data
                                                                                 Control

                                                    Fig 1.3: Components of a CPU



                   A microprocessor is a CPU on a single chip. It is built as an integrated circuit (IC), possibly comprising millions
                   of circuits. A microcontroller is a small computing device consisting of a CPU, RAM, ROM and other peripherals
                   embedded in some other device such as an air conditioner, a washing machine, or an automobile. A microcontroller
                   typically performs a dedicated task without human intervention.



            1.2 Input Devices

            An input device takes input from a user in the form of data or instructions. Some of the commonly used input devices
            are described below (see Fig 1.4):

            1.2.1 Keyboard

            A keyboard is the most commonly used input device. Most of the keys have a symbol printed on them. When a user
            presses a key, it is conveyed to the system. Keys are often used in a combination, for example, when the key with the
            letter A printed on it is pressed, the system gets the character a. However, when the key shift is pressed, followed
            by the key A, while still holding the key shift pressed, the system gets the character A. A keyboard has several special
            keys, each having designated purpose, such as function, direction, and caps lock keys.





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