Basic Computer Organization

                                                   

                            COMPUTER ORGANIZATION

                                                                         

                                                                         

  Ø  INPUT UNIT:

Data and instructions must enter a computer system before the computer can perform any computation on the supplied data. The input unit that links a computer with its external environment performs this task. Data and instructions enter a computer through an input unit in a form that depends upon the input device used. For example, data can be entered using a keyboard in a manner similar to typing and this differs from the way in which data is entered through a scanner, another type of input device. However, a computer’s memory is designed to accept input in binary code and hence, all input devices must transform input signals to binary codes. Units called input interfaces accomplish this transformation. Input interfaces match the unique physical or electrical characteristics of input devices to the requirements of a computer system.

In short, an input unit performs following functions:

(1.) It accepts (or reads) instructions and data from outside world.

(2.) It converts these instructions and data in computer acceptable form. Units called input interfaces accomplish this task.

(3.) It supplies the converted instructions and data to the storage unit for storage and further processing.

                                                               

                                                                        

                                                                  

Ø  OUTPUT UNIT:    

An output unit performs the revers operation of that of an input unit. It supplies information obtained from data processing to outside world. Hence, it links a computer with its external environment. As computers work with binary code, results produced are also in binary form. Therefore, before supplying the results to outside world, the system must convert them to human acceptable (readable) form. Units called output interfaces accomplish this task. Output interfaces match the unique physical or electrical characteristics of input devices (terminals, printers etc.) to requirements of an external environment.

In short, an output unit performs following functions.

(1.) It accepts the produced results, which are in coded form. We cannot understand the coded results easily.

(2.) It converts these coded results to human acceptable (readable) form. Units called output interfaces accomplish this task.

(3.) It supplies the converted result to outside world.

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  Ø  STORAGE UNIT:

Data and instructions entered into a computer system through input units have to be stored inside the computer before actual processing starts. Similarly, results produced by a computer after processing have to be kept somewhere inside the computer system before being passed on to an output unit. Moreover, a computer must also preserve intermediate result for ongoing processing. Storage unit of a computer system caters to all these needs. It provides space for storing data and instructions, intermediate results, and results for output.

In short a storage unit holds (stores):

(1.) The data and instructions required for processing (received from input units).

(2.) Intermediate results of processing.

(3.) Final results of processing, before the system releases them to an unit.

Storage unit of all computers is comprised of following two types.

   (1.) Primary Storage:

Primary storage of a computer system, also known as main memory, stores pieces of program instructions and data, intermediate results of processing, and recently produced results of those job(s) on which the computer system is currently working. The central processing unit can access these pieces information directly at a very fast speed because they are represented electronically in the main memory chip’s circuitry. However, primary storage is volatile, and it loses the information in it as soon as the computer system switches off or resets. Moreover, primary storage normally has limited storage capacity because it is very expensive. Primary storage of modern computer systems is made up of semiconductors devices.

    (2.) Secondary Storage:

Secondary storage of a computer system, also known as auxiliary storage, takes care of the limitations of primary storage. It supplements the limited storage capacity and volatile characteristics of primary storage. This is because secondary storage is much cheaper than primary storage and it can retain information even when the computer system switches off or resets. A computer system user secondary storage to store program instructions, data, and information of those jobs on which the computer system is currently not working but needs to hold them for processing later. The most commonly used secondary storage medium is magnetic disk.

  Ø  ARITHMATIC AND LOGIC UNIT (ALU):

A computer performs all calculation and comparison (decision-making) operations in the ALU. During processing of a job, the computer transfers data and instructions stored in its primary storage to ALU as and when needed. ALU does the processing and the computer temporarily transfer intermediate results generated there back to primary storage until needed later. Hence, data may move back and forth several times between primary storage and ALU before processing of the job is over.

             The engineering design of a computer’s ALU determines the type and number of arithmetic and logic operations that a computer can perform. However, almost all ALUs are designed to perform the four basic arithmetic operations (add, subtract, multiply and divide) and logic operations or comparisons such as, less than, equal to, and greaten than.

  Ø  CONTROL UNIT (CU):

How does an input device of a computer system know that it is time for it to feed data to storage unit? How does its ALU know what should be done with th data once it receives them. Moreover, how it is that the computer sends only the results for output to an output device and not the intermediate results? All this is possible due to the control unit of the computer system.

                       A computer’s control unit does not perform any actual processing of jobs, but acts as the central nervous system for other components of the computer system. It manages and coordinates the operations of all other components, It obtains instructions from a program stored in main memory, interprets the instructions, and issues signals causing other units of the system to execute them.

  Ø  CENTRAL PROCESSING UNIT (CPU):

Control Unit (CU) and arithmetic logic unit (ALU) of a computer system are together known as the Central Processing Unit (CPU). It is the brain of a computer system. Similarly, in a computer system , the CPU performs all major calculations and comparisons, and also activates and control the operations of other units of the computer.