Page 14 - Computer Science Class 11 Without Functions
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Central Processing
                                                           Unit

                                    Input                                      Output
                                    Device                                      Device


                                                       Memory Unit


                               Fig 1.1: Components of a computer system (Von Neumann Architecture)

        The input unit, Central Processing Unit (CPU), memory unit, and output unit constitute the hardware of a computer.
        A sequence of instructions given to a computer is called a program. A computer manufacturer provides several useful
        programs that help the end user to use the computer conveniently. A set of programs that performs a useful task
        is called software. In contrast to the computer hardware, the software is not visible to the human eye. A computer,
        having several input-output devices, is also called a computer system.
        Fig 1.2 presents the IPO cycle ("Input > Process > Output" cycle), which represents the sequential stages through which
        data or actions flow in a system where initial data (input) is transformed (process) to produce a result (output), which
        can then influence subsequent actions (input).



                                                           INPUT




                                                   OUTPUT       PROCESS


                                                     Fig 1.2: IPO Cycle


               Electronic Numerical Integrator and Computer (ENIAC) was the first electronic programmable computer.












        1.1 CPU

        The Central Processing Unit (CPU), also called the processor, is the computer's brain and is responsible for carrying
        out all the processing in the computer system. A CPU is often fabricated as a semiconductor chip, called Integrated
        Circuit(IC). Given a task, the CPU is provided with a sequence of instructions in the form of a program. For the execution
        of an instruction in memory, it goes through an instruction cycle which first fetches the instruction and the data
        (if required) from memory, decodes the instruction (what action to perform), and performs the action. The result of
        the computation may be stored again in the memory. Thus, the CPU controls the entire data flow and instructions
        inside the computer. To facilitate its functioning, the CPU comprises of the following components (Fig 1.3):
           Registers:  While  processing  an  instruction,  the  CPU  needs  to  store  in  its  local  storage  the  instruction,  memory
           addresses being referred during the instruction execution, data operands (on which operation is to be carried out),
           and the result of the computation. For storing and accessing the information mentioned above, the CPU requires high-
           speed temporary storage units, called registers.

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