BASIC COMPUTER ORGANIZATION!
We might be using computers for various applications. Generally, computers perform five basic operations namely: input, storage, processing, output and control. A typical computer must get the input from the user, store it permanently in a memory device, and process the data to produce information as output. It must also control the activities performed by its various units.Input Computers receive data from its users. Users feed data (e.g., reservation details) in to a computer through devices such as keyboard and mouse, called input devices. The given data are then processed by applying a set of instructions, called program. Programs instruct a computer what to do with the data.
Storage The data/program, which are given as input to the computer are then stored in a hard disk. The Processing Unit (CPU) can get the data/instructions from the storage unit whenever required.
Process Arithmetic and Logical Unit (ALU) processes (analyzes) the data available in the storage unit in order to produce useful information. For instance, it may process the request for booking a seat in a particular train on a particular date if a seat is available on the requested date. ALU is the main unit, which performs operations on data.
Output After processing the input, the computer provides the required information (result) to the user. For instance, in a reservation system the output may be a printed ticket or display of some information like no. of seats available on a particular date. Commonly used output devices are monitor, printer and plotter.
Control All computers have a control unit that controls the manner and sequence of operations. The control unit and the ALU form the Central Processing Unit (CPU) of a system.
Fig. : Functional Organization of a Computer
The various building blocks of a computer are explained below:Input Unit:
Input Unit consists of one or more devices, which are used for inputting data and instructions into a computer. Keyboard is the commonly used input device. Other input devices are mouse, scanner, light pen etc. Regardless of the type of input device, all input devices perform the following functions:
- Accept input from the outside world.
- Convert the input to a form that computer can understand.
- Supply the converted data to the computer system for further processing.
Storage Unit:
The storage unit consists of a set of storage devices that store data permanently for later use. For instance, one may like to save a business letter for later reference. The storage devices used in a computer system are classified into two categories – primary storage and secondary storage.
The primary storage (also called the primary memory or main memory) stores and retrieves information very fast. This storage device is generally used to hold programs and data, which are being processed by the CPU. It also holds the data being received from the input unit and the intermediate and final results of the program being executed. This memory is volatile in nature, and hence it looses its contents when the power goes off.
The secondary memory is used like an archive that can hold data and instructions permanently. The program to be executed by CPU is first transferred from the secondary memory to the primary memory before its execution. Similarly, after execution, the resultant data are transferred back to the secondary memory for later use. The secondary memory is slower and cheaper than the primary memory. Examples for secondary memory devices are: Floppy diskette, zip diskette, hard disk and magnetic tape.
Output Unit:Computers store data and instructions internally in binary form. The input given by the user is converted into binary form in order to perform any processing on it. After processing, the binary data must be converted back to the form understood by the users. This task of converting and delivering the required output in human readable form is done with the help of an output device. Printer and Video Display Unit (VDU; also called Display Screen) are commonly used output devices.
Arithmetic-Logic Unit (ALU):
All calculations are performed in the Arithmetic-Logic Unit (ALU) of the computer. The ALU performs basic operations such as addition, subtraction, multiplication and division. It also performs logical operations such as comparing one number against another and checking if ‘A’ is less than, equal to or greater than ‘B’.
In order to perform a computation by ALU, the control unit first transfers the required data from the storage unit to ALU and allows ALU to perform the required computation. After performing the computation (arithmetic or logical operation), the result is transferred from ALU to the storage unit.
Control Unit:
The control unit controls all other units of a computer. For instance, the input unit does not know where to send the data after it receives input from the user. The control unit gives necessary instructions to the input unit to send the input to the storage unit or to the VDU. In the same way, it controls the flow of data and instructions between the ALU and the storage unit. The control unit also controls what should be sent to the output device and when.
