introducation to computers

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UNIT - I : 




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A computer is an electronic device which accepts data from an input device processes it and gives information to output device Data  Unordered Form. (raw material form) Processes  Work. Information  Ordered Form

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The word computer comes from the word “compute” which means to calculate. It is called as calculating device that performs arithmetic operations at enormous speed. A computer is a device that operates on data. A computer can store, process and retrieve data as and when required. The fact that computers process data is so fundamental that’s why many people have started calling computer as data processor. The activity of processing data using a computer is called data processing.

Diagram of a Computer : 

Diagram of a Computer Monitor Key board Speakers Mouse C P U (Central Processing Unit )

Input and Output Devices : 

Input and Output Devices

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Input devices From which devices you are accepting the data those devices are known as input devices Ex:- Keyboard, Mouse, Scanner, OCR, MICR, etc.., Output devices From which devices we are getting the information those devices are know as output devices Ex:- Monitor, Speakers, Printer Etc..,



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Keyboard:- This is the most commonly used input device, this device accepts set of characters and translate them into a form, which computer can understand. Keyboard consists of 104 keys. Mouse:- Mouse is a small hand held device, that fits in the users palm. It is the most popular pointing and drawing device. This device is used to move the cursor on the computer screen to give the instructions to your computer and to run the programs or applications. It is also used to select menu commands, move icons, re-size windows and for closing windows.

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Scanner:- This device is used to input pictures and images into your computer. It converts images to digital form so that it can be fed into the computer.

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Optical Character Recognition (O C R):- The computer cannot interpret the stored document as letters, number and special characters. So in order to over come this problem we are using the technology OCR. This device converts the bit map images of characters to equivalent ASCII codes. OCR software is designed to recognize texts which are in OCR fonts. If the document contain different types of fonts, the OCR software will not work effectively.

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Magnetic-ink character recognition (MICR):- MICR is similar to OCR, which is used by the banking industry for fast processing of large volume of cheques. Before giving cheques to the customers, bank identification code (name, branch etc.), identification number and cheque number are printed in special characters with special ink, which contains magnetizable particles of iron oxide. The MICR supported character set which contains only symbols i.e. 0-9(10 digits) and 4 special characters



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Monitor:- It is a output device used to display the information, programs and applications. It is also called as VDU (Visual Display Unit). Like television, monitors are also available in different sizes. Speakers:- It is also a output device, used to produce music or speech from programs. A speaker port allows to connect speaker to the computer. Speakers can be built in or we can attach separately.

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Printer:- It is also a output device used to generate a hard copy of files. There are two types of printers depending upon their qualities (1) resolution (2) print speed. Print resolution is measured as the number of dots per inch and print speed is typically measured in pg’s minute.

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Types of printers:- Drum Printer. Chain/Brand Printer Dot-Matrix Printer. Inkjet Printer. Laser Printer.



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Speed Storage (or) Memory Accuracy Diligence Versatility

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Speed:- Computer is a fast calculating device, that performs in few seconds, that a human can do in an entire year. The units of speed in case of computers are micro seconds, nano seconds and Pico seconds. Memory:- Computer can store and recall any amount of information because of its secondary storage capacity. Even after several years, the information recalled would be accurate as on the day when it fed to the computer. It forgets or looses certain information only when it is asked to do so. The units of memory is in bytes.

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Accuracy :- The accuracy of a computer is consistently high and the degree of accuracy depends upon its own design. It will perform every operation with same accuracy. It can produce accurate results at a high degree of 100%. Diligence:- Computer is free from monotony, tiredness, and lack of concentration. It can work continuously for hours without errors. If 10 million calculations has to be performed, a computer can perform the 10th million calculation exactly with same accuracy and speed as first one.

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Versatility:- Computer can be used to solve the problems related to different fields like commercial, scientific, educational, research and defense. This is one of the most wonderful things about the computer. In one moment, it is preparing the results of an examination, the next moment, it is busy in preparing electricity bills and in between it may be helping an office section to trace important letters.



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No IQ:- It cannot think by its own. A computer cannot take its own decisions. It has no intelligence. Its IQ is zero. Computers cannot make judgments of their own. The judgments is based on the instructions given to them in the form of programs that are written by us. No feelings:- Computers are devoid of emotions. They have no feelings because they are machines.

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Central Processing Unit (CPU)

Memory Unit : 

Memory Unit They are two types of memories Primary Memory. Secondary Memory or Auxiliary Memory. Primary memory:- RAM & ROM comes under primary memory. RAM (Random Access Memory) ROM (Read Only Memory)

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RAM (Random Access Memory) :- It is the key working area of the memory, also called as user memory. It varies from computer to computer and it determines the sizes and scope. The main feature of RAM is that can be read from or written onto and can be accessed automatically. The contents of RAM are available as long as the computer is not switched off, it loses the contents as soon as the power is switched off. So this is a volatile memory or temporary memory and the data that is stored here can be altered.

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ROM (Read Only Memory) :- As the name itself implies, it holds permanent data or instruction that can be read from, but not written on to, i.e. information is permanently recorded. So that user cannot change the instructions. It is a non-volatile memory, it means that the contents of ROM are not lost when the computer is switched off. ROM’s are also known as field stores, permanent stores or dead stores. They are two varieties of ROM’s PROM (Programmable Read Only Memory) EPROM (Erasable Programmable Read Only Memory)

Secondary Memory or Auxiliary Memory:- : 

Secondary Memory or Auxiliary Memory:- This memory is again divided in to Sequential access device and Direct access devices. Magnetic tape comes under sequential access device. Magnetic disks and optical disks comes under direct access devices. Floppy disk and Hard disk comes under magnetic disks. CD comes under optical disks.

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Magnetic tapes:- It is the most popular storage medium for storing large amount of data. Magnetic tape medium is a plastic ribbon which is of ½ inch or ¼ inch wide, 30-2400 feet long. It is coated with magnetized recording material such as iron oxide or chromium dioxide. Data is recorded on the tape in the form of tiny invisible magnetized and non-magnetized spots on the surface of the tape.

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Magnetic disk:- It is a thin, circular plate made of metal or plastic, coated on both sides with a magnetized recording material such as iron oxide.

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Floppy disk:- Floppy disk is used to storage purpose the data and to transfer the data from one location to another location. This device provides the option to read or write data. The memory capacity of a floppy is 1.44 MB (Mega Bytes), size of a floppy disk is 3 ½ sq inches. Data storage will be in the form of tracks and sectors Demerits:- These are light-protecting disks so, it is better to kept at dark places. It will be affect on magnetic rays so better to avoid magnetic devices near by these devices.

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Hard disk:- It is not a single flexible disk, but a stack of metal disks sealed in box. The storage capacity of the hard disk can be from 2 GB to 120+ GB. These are very reliable as compared to floppies. It is rewritable and any information can be accessed in a fraction of second.

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Optical disk:- It is a high capacity secondary storage medium. It can store extreme large amounts of data in a limited space. An optical disk consists of rotating disk, which is coated with a thin metal. Laser beam technology is used for recording/reading of data on the disk. Due to the use of laser beam technology, optical disks are also known as laser disks or optical laser disks.

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Compact disks:- Compact disk contains digital information which can be read or write. It can hold vast amounts of information such as full-motion videos, animation, music etc., The memory capacity of CD is 700 MB. Data storage is in the form of microscopic pits or particles. Size – 12 cm in diameter. Due to its light weight, they are very easy to handle, store and transport from one place to another.





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Computer languages are basically divided in to 3 categories. Machine language Assembly language. High level or user level language

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Machine level language:- This language is also known as low level language or binary level language. This language contains combinations of 0’s and 1’s. It is an system understandable language.

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Assembly language:- This language is in the form of alphanumeric mnemonic codes. This language that allows instructions and storage locations to be represented by letters and symbols instead of numbers. This is a machine dependable language. Knowledge of hardware is required. Assembler:- it is a translator program that translates the assemble language program into machine language program.

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High level language:- This language contains English alphabets, numbers and mathematical symbols. This is a machine independent language. There is no need of dealing with machine level coding. In order to translate high level language to low level language. There are two converters namely 1) Complier 2) Interpreter

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Complier:- It is converter which is used to convert high level program to low level programs. It follows the procedure of at a time checking. Interpreter:- It is also a converter which is used to convert high level program to low level programs it follows the procedure of line by line checking.

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ASCII Code (American Standard Code Information Interchange):- ASCII-code is a "languages of digital devices", devices like computer or digital television A  65, B  66……… a  97,b  98………...



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Algorithm:- It is a step by step description of how to arrive at the solution of the given problem. It is also defined as sequence of instructions designed in a manner such that desired results will be obtained. There are various ways to represent an algorithm. Normally programmers use one or more of the following ways to represent their algorithms As program. As flow charts. As pseudo codes.

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Flowcharts:- A flowchart is a pictorial representation of an algorithm. It uses boxes of different shapes to represent different types of instructions.

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Basic Flowchart Symbols:- Processing

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Principles or rules of a flow chart:- First chart the main line of logic, then incorporate detail. Words in flowchart symbols should be common statements, which are easy to understand. Be consistent in using names and variables in flowchart. Go from left to right, which top to bottom in constructing flowcharts. Keep the flowchart as simple as possible. If a new flowcharting page is needed it is recommended that the flowchart be broken at an input or output point

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Limitations:- Flowcharts are very time consuming. There are no standard determining the amount of detail that should be in closed in a flowchart. Re drawing a flowchart being a tedious task. Programmers do not redraw the flowchart ,when the program is modified



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BIT :- It is small memory location which can able to store either 0 or 1. 4 Bits = 1 Nibble 8 Bits =1 Byte. 1024 Bytes = 1 Kilo Byte (KB). 1024 kilo Bytes = 1 Mega Byte (MB). 1024 Mega Bytes = 1 Gaga Byte (GB).



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Computer virus:- A virus is a program, that can infect other program by modify them. The modification includes creating a duplicate copy of the virus program, which can infect other programs. Virus takes a temporary control of operating system. When the infected software comes into contact with an uninfected software, a fresh copy of a virus passes into the uninfected software. Thus the infection can be spread from one software to software or computer to computer. A virus can do anything that other programs do. The only difference is, it attaches itself to another program and executes secretly when the host program is running. Once a virus is executing, it can perform any function.

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Types of virus are:- 1)Parasitie virus. 2)Memory Resident virus. 3)Stealth virus. 4)Polymorphic virus.



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Computer consists of two basic parts 1) Hardware. 2) Software. Hardware :- Physical components of a computer is known as hardware. Hardware is the term given to the machinery and the various individual pieces of the computer. Hardware components which we can touch and we can able to see each and every part. Ex:-Keyboard, Mouse, Monitor, CD Drive, Printer and all visible parts inside CPU.

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Software:- Computer cannot do anything on its own. It must be instructed to do a desired job. Hence it is necessary to specify a sequence of instructions to do our job. This sequence of instructions is known as program. The group of programs forms a software.

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Software is divided in to two types 1) System Software 2) Application Software. System software:- It is software designed to control the operations and to increase the processing capabilities of the computer. It makes the computer system more effective and efficient. All the operating systems are system software's. Application software's:- Programs developed for solving specific problems through a specific task is known as application software.



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OPERATING SYSTEM (O.S):- O.S is a system software which acts as a interface between user and computer. The work of O.S is to control the resources of the system and provides its users more convenient to use. Functions of operating system:- Process management:- it includes scheduling of various system resources to the different processes, and providing communication between the processes. Memory management:- it includes allocations and de –allocation of memory space to various programs.

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File management:-it take care about file related activates such as organization, storing, retrieval, naming sharing and protection of files. Security:- operating system protects the resources and information of a computer system against destruction and unauthorized access. Not only the above it is also responsible for batch processing, time sharing, checking of errors and loading, executing of user programs etc.,

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Operating system is divided in to two types:- Single user operating system Multi user operating system. Single user operating system:- As the name specifies, One user using one system at a time is known as single user operating system Example:- MS-Dos, Windows 95,98, 2000, XP, etc., Multi user operating system:- As the name specifies many users using single system at a time is known as multi user operating system. Example:- Unix, Linux, Win NT etc..,

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MS-DOS (Microsoft Disk Operating System):- It is a single user operating system introduced in the year 1981 jointly by Microsoft and IBM. It become most popular operating system in 1980’s for personal computers. Its popularity started reducing in the year 1990’s due to the launch of Microsoft Windows Operating System. Unix Operating System:- It is a multi user operating system, developed in early 1970’s . It is the first operating system to be written in high level language ‘C’. This operating system become popular due to the concept of ”porting” .

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Microsoft windows operating system :- This operating system was developed by Microsoft to overcome the limitations of own MS-DOS. The main important features are It is a graphical user interface. (GUI) Hence it is easier for a new user to learn and use the system. It is single user multitasking operating system. That is a user may run more than one program at a time. The monitor screen can be partitioned into multiple windows and the progress of different programs can be viewed on different windows. The first successful version of windows is 3.0, windows 95, 2000, XP, Vesta.



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Historians start the history of calculation with “ABASCUS” (a calculating device) in around 5000 B.C. John napier a Scottish mathematician, did considerable work on aids for calculation and invention of algorithms in 1614. In 1620, Willam oughtre, an English mathematician invented the slide rule. In 1642 Blaise pascal, French mathematician invented the Ist mechanical calculating machine. In 1671 gottfried von leibnitz, a German mathematician invented a calculating machine which was able to perform multiplications and divisions

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In 1822 Charles Babbage a professor of mathematics at Cambridge university designed a machine called difference engine. This machine can perform simple computations for trigonometry and logarithmic tables. After Second World war II, Howard H. Aiken of Harvard university designed a machine that can automatically perform a sequence of arithmetic operations; After that ENIAC ( Electronic Numerical Integrator and Calculator) was developed in 1946, was the first electronic calculator. In between 1947 and 1950, the more school personnel and the Billistics research laboratory of U.S army built a computer named EDVAC (Electronic Discrete Variable Automatic Computer).

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Neumann (frequently referred as the father of modern computers) was to introduce the stored program concept in a computer. After that generations started…..,



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FIRST GENERATION:- Vacuum tubes technology. Limited storage capacity. Slow in speed. Huge in size and produces over heat.

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SECOND GENERATION:- Transistors and diodes technology. Increase in storage capacity Faster in speed Reduction in size and heat production

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THIRD GENERATION:- Integrated circuits technology (I C’s). Smaller in size and better in performance. Extensive use of high level programming. Remote processing and time sharing.

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FOURTH GENERATION:- Large scale integration technology circuits. (V L S I) Increased in storage capacity. Faster and smaller. Modular design, Versatility and compatibility. Sophisticated programs and languages for special applications.

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From the above, we can find computers were very big and consumed a lot of power, heat up tremendously and shut down frequently. Because of all these they are very expensive to build and maintain. As the technology improved computer became smaller and smaller, they became more faster and more powerful.

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Power supply box (SMPS) R A M Mother Board Processor C D Drive Floppy Drive Hard disk



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