Computer System

A computer system is the combination of Input unit, Processing unit, the output unit and the Memory Unit which work in co-ordination with each other to extract a meaningful output(Information) after processing the Raw Data(Input) given by the user.

                                                  Fig: A complete Computer System

Input Unit
The input unit includes all the devices and process involved in sending input into the computer system. Different input devices like Keyboard, Mouse, Joystick, light pen, microphone, etc are used in a computer system in order to send data and instructions into the computer. Some of the major Input Devices are:

Keyboard
Keyboard is a primary Input device that is used for entering different text and instructions into the computer. It is an electronic input device that contains different keys in it, by pressing on which different raw data is fed into the memory of the computer. Normally, there are two types of keyboard namely, Normal and Multimedia but according to the model they are classified into three categories:
XT (Extended Technology): having 83 Keys
AT (Advanced Technology): having 101 Keys
Enhanced Keyboard: having more than 101 keys

Mouse
Mouse has become an indivisible part of the GUI based Operating system due to its click and work Environment. It normally contains three buttons left, right and scroll. There are three types of mouse available in the market.
Mechanical Mouse(plastic or metallic ball and mechanical detection)
Opto-Mechanical Mouse (metallic ball but laser detection)
Optical Mouse (Emits laser & moves the cursor to the direction the mouse is moved)
Among these the most popular nowadays is the optical one.
Different USB and wireless mouse and keyboard are also increasingly used by many users today.
Joystick
Joystick is another important input device normally used for gaming purpose. It has been developed as an important device for computer gaming. It is also used for simulations. It contains a hand held stick which can freely be moved around to move the graphical objects and different buttons to control the movement of the object. It may or may not contain the stick. In some cases it contains more buttons instead.

Scanner
Scanners are the devices that are used to convert the analog pictures, graphics and text to digital and store it in the computer. It has been very popular for scanning different governmental and official documents to send the original like copy from one place to the other. It is also used to scan different signatures, fingerprints etc. Its main purpose is to keep photographic records of different documents

Output Unit
The output unit includes all the devices and process involved in displaying the output of  the computer system through different output devices like Monitor, Printer, Plotter, Speaker etc. The Output Devices are divided into two categories:

Softcopy output Devices

Such devices are said Softcopy output Device which can display output but cant be easily accessible to the users to touch or feel. Users can only see or to the output temporarily on the screen through these devices. For example: Monitor, projector, speaker etc.

Monitor
Monitor is the most important softcopy output device whose structure is similar to that of a television. It is also Known as VDU (Visual Display Unit) All the information generated by the computer is displayed through the monitor. It provides visual interface for the users to work with different graphics or pictures or something else. Monitors are also classified into three categories:
CRT (Cathode Ray Tube)
LCD (Liquid Crystal Display)
PLASMA

Hardcopy output devices
That device whose output is printed on a paper and is accessible for the users to touch or feel is known as Hardcopy Output Device. It is usually permanent and can take just the output from one place to other. For example, Printer, Plotter, COM (Computer Output to Microfilm)

Printer
Printer is the device that is used to make a copy of different text and pictures on the paper. It is a hard copy output device as we get the output of the computer printed on a paper through Printers. Printers are also categorized into two types:
i) Impact printer
The printer that prints the text and pictures on a paper by striking a head or a needle against the paper is known as impact printer. For example Dot matrix printer, Daisy wheel printer etc.
ii) Non-Impact Printer
The printer that prints the text and pictures on the paper without having contact of any devices with the paper is known as non-impact printer. These type of printer use thermal technology (heat) to print on the paper.

Plotter
Plotters are also the hard copy output device similar to printer which is used to print only the large maps and other engineering designs.

Central Processing Unit (CPU)
The CPU is the main computing part of a computer which is often regarded as the brain of a computer. The CPU lies at the Motherboard/PCB (Printed Circuit Board) inside the CPU casing with which all the peripherals (Monitor, Keyboard, mouse, printer, speaker, memory devices etc.) of the computer are connected. The CPU controls and co-ordinates the entire computer system. It is composed of three units:

Control Unit
The Control unit is the part of the CPU that is responsible for the execution of different instructions. It controls the flow of data and instructions within the entire Computer System.

Arithmetic and Logical Unit
The ALU is responsible for the manipulation of different Arithmetic (Mathematical) and Logical operations overtaken by the computer.

Memory Unit (Primary Memory)
Primary Memory is the workspace of the computer that holds the currently running programs and other necessary information of the computer. They are divided into two types:

i) RAM (Random Access Memory) is high speed semiconductor memory where the system files and other currently running programs are stored temporarily for performing different operations. RAM is known as a volatile memory because the data or programs stored in RAM is automatically erased when the electricity supply is cut off or the computer is turned off. Basically there are two types of RAM viz. DRAM (Dynamic RAM) and SRAM (Static RAM).
ii) ROM (Read only Memory)
ROM is a type of memory that stores the system information written into it by the manufacturer. The programs (instructions) written in ROM is known as firmware. The Data or instructions in it can neither be erased nor added.

Secondary Memory
Secondary memory includes the memory devices that are used to store a huge amount of data for future use. The data or information stored in the secondary storage devices is not lost until the devices are damaged. It is very useful for backing up critical documents and different software programs. The secondary storage devices are also known as Auxiliary storage devices. Example Hard Disk, Pen Drives, CD, DVD, Memory Card etc.
Computer Architecture

The organization of Hardware and Software in a computer system is known as Computer Architecture, i.e. a computer is composed of different Hardware and the Software Components.

                                         Fig: Basic Architecture of a Computer.

Hardware
Hardware are the physical components of a computer that we can touch or feel. All the devices connected to the computers are known as hardware. For example Motherboard, Processor, Keyboard, Mouse, Monitor, Casing, Hard disk, pen drives etc. Hardware are the devices that prepare framework for the computer software to function properly.

Software

Software can be termed as the life of the computers. It is actually the set of instructions that controls different task of the computer and makes the computer to work. They are the guidelines for the hardware devices to perform different task. Basically there are two types of software.
A) Application Software
Application software are the programs that are written for performing some particular operation on the computer with the help of the system software and other utilities. They are the programs which actually perform the manipulative task in the computer. Any application software requires the operating system to run. Ms Word, Excel, Photoshop, Tally, Dreamweaver, Accounting software etc are the commonly used Application Software.

B) System Software
An operating system is a set of program that prepares an interface for the users to run application programs in the hardware devices. It controls and co-ordinates all the hardware components of a computer and make the application software able to run in the computer hardware. A computer may run without the application software but it is impossible for a computer to work without System Software.  There are two types of operating system. They are:
i) CUI (Character/Command User Interface)
ii) GUI (Graphical User Interface)
The operating system like Ms DOS, Linux fall under the CUI based operating system while the operating system like Windows, Red Hat Linux etc. fall under GUI based operating system.
Ms Dos (Microsoft Disk Operating System) is one of the CUI based Operating Systems which needs different commands to function. User has to write different commands to make the computer work in this operating System. It does not support multitasking and multi processing environment.

Windows Operating System
Ms Windows is a very popular and the best Operating System available in the whole world supports any kind of computer software or hardware built so far. It provides a graphical environment to perform different operations which has made it user-friendly. Any person who doesn't know enough about the computer can also operate in the windows operating system.

Windows Vista (Black Edition 2009)
Windows Vista Ultimate Black Edition TM 2009 is one of the latest versions of Windows operating system which provides an easy and efficient method to operate on the computer. Its Graphics Quality is very high and is much secure than any other previous versions of windows. Different added features like the windows sidebar, easy searching facility, rich set of attractive desktop background and themes, many useful Gadgets are some of the important feature of windows vista. Features like speech recognition, windows narrator, easy to access, and parental control make it easier for the operators to perform different task.

                                              Fig: Desktop of Windows Vista Black Edition.