Basic Computer Organization

 A computer is an electronic device, which can input data, process it, store the intermediate results and display output. All computer systems perform the following five basic operations: 

1. Input. The process of entering data and instructions into the computer system. 
2. Storing. Saving data and instruction for future use in the memory of a computer is called as storage. 
3. Processing. Performing arithmetic and logical operations on the data to produce some information is called as processing. 
4. Output. The process of producing the result on paper or on screen is called as outputting. 
5. Controlling. Directing the manner and sequence in which all of the above operations are performed. 

The basic organization of a computer can be very easily depicted with a block diagram. The solid lines indicate the flow of data and information and the dotted lines represent the control exercised by the control unit. It displays five major building blocks or functional units, of a digital computer system. These five units correspond to the five operations performed by all computer systems. 

Input Unit

Data and instructions must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit, which links the external environment with the computer system. Data and instructions enter input units in forms that depend upon the particular device used. For example, data is entered from a keyboard in a manner similar to typing, and this differs from the way in which data is entered through a card reader, which is another type of input device. However, regardless of the form in which they receive their inputs, all input devices must provide a computer with data that are transformed into the binary codes that the primary memory of a computer is designed to accept. Units called input devices accomplish this transformation. Input interfaces are designed to match the unique physical or electrical characteristics of input devices to the requirements of the computer system.

Functions of an input unit 

1. It accepts or reads the list of instructions and data from the outside world. 
2. It converts these instructions and data in computer acceptable form. 
3. It supplies the converted instructions and data to the computer system for further processing. 

Output unit 

The job of an output unit is to supply the information and result of computation to the outside world. Thus it links the computer with the external environment. As computers work with binary code, the results produced are also in the binary form. Hence, before supplying the results to the outside world, it must be converted to human acceptable form. Units called output interfaces accomplish this task. Output interfaces are designed to match the unique physical and electrical characteristics of output devices to the requirements of the external environment. 

Storage unit

The data and instructions that are entered into the computer system through input units have to be stored inside the computer before the actual processing starts. Similarly, the results produced by the computer after processing must also be kept somewhere inside the computer system before being passed ion the output units. Moreover, the intermediate results produced by the computer must also be preserved for ongoing processing. The storage unit or the primary /main storage of a computer system is designed to cater to the needs of storage. It provides space for storing data and instructions, space for intermediate results, and also space for the final results. 

Arithmetic and logic unit

The Arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of these instructions takes place during the processing operation. To be more precise, all calculations are performed and all decisions (comparisons) are made in the ALU. The data and instructions, stored in the primary storage prior to processing, are transformed as and when needed to the ALU where processing takes place. No processing is done in the primary storage unit. Intermediate results generated in the ALU are temporarily transferred back to the primary storage until needed at a later time. Data may thus move many times before the processing is over. After the completion or processing, the final results, which are stored in the storage unit, are released to an output device.

The type and number of arithmetic and logic operations that a computer can perform is determined by the engineering design of the ALU. However, almost all ALU's are designed to perform the four basic arithmetic operations - add, subtract, multiply, divide and logic operation or comparison such as Less than, greater than, equal to, not equal to etc. 

Control unit

Some questions may arise in your mind.

How does the input device know that it is time for it to feed data into the storage unit? How does the ALU know what should be done with the data once they are received? And how is it that only the final results are sent to the output device and not the intermediate result? All this is possible because of the control unit of the computer system.

• By selecting, interpreting, and seeing to the execution of the program instructions, the control unit is able to maintain order and direct the operation of the entire system. 
• Although, it does not perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer.
• It manages and coordinates the entire computer system. 
• It obtains instructions from the program stored in main memory, interprets the instructions, and issues signals that cause other units of the system to execute them. 

Central processing unit

The control unit and the arithmetic logic unit are jointly known as the central processing unit (CPU). The CPU is the brain of any computer system. In a human body, the brain takes all major decisions. Similarly, in a computer all major calculations and decisions are made inside the CPU and the CPU is responsible for activating and controlling the operations of other units of a computer system.

Computer as a system

A system is a group of integrated parts that have common purpose of achieving some goal. So is a computer, which is made up of integrated components (Input, Output devices, storage unit, CPU) that work together to perform some task or goal. 

Points to Remember

• A computer is an electronic device, which can input data, process it, store the intermediate results and display output. Input. The process of entering data and instructions into the computer system. 
• Storing. Saving data and instruction for future use in the memory of a computer is called as storage. 
• Processing. Performing arithmetic and logical operations on the data to produce some information is called as processing.
• Output. The process of producing the result on paper or on screen is called as outputting. 
• Controlling. Directing the manner and sequence in which all of the above operations are performed. 
• Data and instructions must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit, which links the external environment with the computer system. 
• The job of an output unit is to supply the information and result of computation to the outside world. 
• The storage unit or the primary /main storage of a computer system is designed to cater to the needs of storage. It provides space for storing data and instructions, space for intermediate results, and also space for the final results. 
• The Arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of these instructions takes place during the processing operation. 
• The control unit and the arithmetic logic unit are jointly known as the central processing unit (CPU). 
• A system is a group of integrated parts that have common purpose of achieving some goal.