1. The Computer System

2. CLASSIFICATION OF COMPUTERS BY SIZE
Classified into 5 groups
Mobile computers
2. Microcomputers
3. Minicomputers
4. Mainframes
5. supercomputers

3. Mobile computers
Mobile computers are the smallest computers designed to be carried by the users.
Eg: Laptop, Tablet, Smartphone, PMP, E-book reader

4. Microcomputers
A microcomputer is a small computer used by one person at a time.
The desktop computers that we can see in most office, schools, colleges, and home are microcomputers.
It is also called as personal computers or PCs.

5. Minicomputers
It is larger than microcomputers, as same to the size of refrigerator.
It first appeared in the year 1960’s.
In 1980s they got replaced by microcomputers.

6. Mainframes
Mainframes are big, powerful, and expensive multiuser computers.
It is mainly used for bulk data processing in large organizations like offices,airlines, and banks.

7. supercomputers It is biggest and most powerful computers.
They often occupy the whole room.
They can process trillions of instructions per second.
Government organizations & large industries use this computers. eg; To find weather forecasting.

8. COMPONENTS OF COMPUTERS
TWO MAIN COMPONENTS
Hardware
Software

9. HARDWARE
The physical components of a computer system that we can see and touch are called hardware.
Eg: Input & output devices, storage devices, CPU

10. INPUT DEVICES
Input devices accept input from the user and convert it into a form that the computer can understand.
supermarkets, banks, etc use specialized input devices to collect large amounts of data rapidly.
Such devices include bar code,magnetic ink character readers, optical character readers, and card readers.

11. BAR CODE READER
A bar code is a unique combination of vertical bars that represents product information, such as price, place of manufacture etc.
The cashier use the bar code reader.

12. MAGNETIC INK CHARACTER READER
MAGNETIC INK is a special ink that contains magnetic particles of iron oxide.
It can scan characters printed in magnetic ink.
This technique is called Magnetic ink character recognition(MICR).
It is used in cheques.

13. OPTICAL CHARACTER READER
An Optical character reader is a device to input normal printed or hand-written text.
Optical character reader
OMR sheet

14. CARD READER
Card readers are used for reading information stored on cards, such as
magnetic strip cards
smart cards.

15. MAGNETIC CARD READER
A magnetic stripe reader, also called a magstripe reader, is a hardware device that reads the information encoded in the magnetic stripe located on the back of a plastic badge.

16. SMART CARD READER
It looks like magnetic strip cards but contain a small chip instead of a magnetic strip.

17. OUTPUT DEVICES
Output devices conveys information from the computer to the user.
Example:
1. LCD projectors
2. Braille printer
3. Plotter

18. PLOTTER
They are commonly used in Computer Aided Design(CAD) and Computer Aided Manufacturing(CAM) for printing plans for house, car parts, machinery, etc.
Plotters are four types
Drum plotters
Micrographic plotters
Inkjet plotters
Flatbed plotters

19. SOFTWARE
The term Software refers to the computer programs that are needed for running or operating a computer system.
Software is often divided into two categories. 

20. SYSTEM SOFTWARE
Systems software refers to programs designed to control the operation of a computer system.
It includes the 
1. operating systems,
2. drivers,
3. compilers,
4. interpreters,
5. assemblers.

21. APPLICATION SOFTWARE
Applications software includes programs that do real work for users. For example, word processors, spreadsheets, and database management systems fall under the category of applications software.

22. COMPUTER LANGUAGES LOW-LEVEL LANGUAGE
It is also called a Programming language, is a language used to write and develop software programs for the computer. It is classified into two categories-
1. MACHINE LANGUAGE
Each instruction is written in the form of a long string of 0s and 1s.
2. ASSEMBLY LANGUAGE
It was the first computer language to use words made with letters of the English alphabet.
HIGH-LEVEL LANGUAGE
It is also called a source program. It cannot run directly on the computer. It must be compiled or interpreted first.
Eg:BASIC, COBOL, FORTRAN, C, C++ AND Java.