Need Of an Operating System.

             

Operating System Need:-

                                                    An operating system Plays an important role of managing software, processes, security, I/O, files etc.In multitasking system every process need to access CPU, memory and storage.When we need to access any program then it will firstly copy into the main memory then after that it will execute and after execution it will save into hard disk, so this work done by the operating system. Operating system hide all these information from the users.  In earlier system user had no idea about the internal structure of computer system. They had to design the application according to the internal structure of the system. but now a day it transparent to the user.   

Usage of operating system:-

- Allow user to execute program and communicate with the computer.
- Interaction between hardware and user.
- Loading program in memory.
- Schedule program in main memory.
-Manage CPU cycle.
-manage Memory.
- Provide Security.

Operating System Functions and services

Operating System:-
                                The responsibility of an operating system is to manage all resources in an efficient manner. So that more then one user can make of these resources simultaneously to get their work done as efficient as possible.
                               
                                 Operating system  provide an interface between hardware and users.

Operating System Services:-
 
              Following are the services that are provide by the operating system-

1.- I/o operation:- 
                               Input output operation mean to read and write operation with the program.During execution program requires input and output devices. So it is the service of operating system to provides these devices to the program. Because operating system hide these all information from the users.It is vary compulsory to provide the access of the required devices when it required, otherwise program will not be completed. Mean it is the services of operating system to give the access of the devices so that program can complete its work.

2- Program execution:- 
                                       The main purpose of operating system to provide a platform to both the program and users. When we put a job for execution in a system then during execution it may require many kind of devices like input devices for read the data and after completion it may require some output devices like printer. So these all activities encapsulates as a process. After completion of the process it will store to the hard disk. So user does not have to worry that how much memory it require . mean memory allocation de-allocation is done by operating system. Overall how to load a program in the memory, execution.  operating system all handle the situation of deadlock (it is the situation when one process require a resource but at that this resource is hold by another process. For example  see the fig given below. In which you can see that there are two process P1 and P2 and two resources R1 and R2. Where situation is P1 request for R2 resource but at that time that resource is hold by P2 and P2 request for R1 but at that R1 is hold by P1. Both P1 and P2 require both of the resources to complete its work . But according the situation it cant be completed it. so this is deadlock situation . Which is also handle by OS.  ).
                                           

3. Communication:- 
                                  Communication is the services that is also provide by the operating system. In multitasking system there are various process that can run on a computer system. During execution of any program they need to communicate with each other for exchange of the information. they can share with each other with shared memory or by the message passing.

4. File system Manipulation:-
                                                 While execution there is need to open a file and read or write a file., saving or deleting a file from disk. This is important service that is also provide by the operating system. operating system also provide the service to that back of file system.

5:-  Error handling:- 
                                  This is  the service of operating system to detect all the error and fix all these for a smooth work.You all knows that  in system there are various ways for error. That can  occur at anytime and anywhere.Operating system aware of these all error. It s the function of operating system for consistent computing.

6:- Resource management (Allocation):-
                                                                  For a process how much time it require to complete its work how much memory it require these all thing is done by operating system. With the help a scheduling technique it schedule all these things. For execution of any process it firstly copy into the main memory. So it is the service of operating system that how much memory does it require in main memory. After completion of a process  it will store in hard disk.

Function of operating system:-

-Main memory management.
-Process Management.
-File Management.
-I/o System Management .
-Secondary storage Management.
- Protection system.
-Command- Interpreter System.

PRINTERS

Printer- Printer is an output device that can help us to print symbols, characters, and also use for some graphic purpose. From printer we got the hard copy. It is basically accept text and graphics output from a computer system and transfers them on to the the paper that is called hard copy. The main printer qualities are color, resolution, speed, memory . There is a figure that shows the laser jet printer.


There are two type of printers Impact and Non- Impact printer.

Impact printer- An Impact printer has mechanism to make contact with the paper. It forms characters or images by striking a mechanism such as pressing an inked ribbon against the paper using a hammer or pins. Following are the example of Impact printer-

Dot-Matrix Printer, Daisy-Wheel printer, Drum Printer, Chain Printer, Line Printer etc.


I- Dot-Matrix printer:- The Dot- Matrix printer uses print heads containing from 9,18, or 24 pins that strike an inked ribbon. That offers the best quality. These Pins produce patterns of dots on the paper to form the individual character. Dot Matrix printer print about 50-500 Character per second (cps). The 24 pin dot matrix printer produce more dots then the 9 or 18 pin dot matrix printer. Which result the better quality. there is also a color ribbons but there is limited use of color. The main drawback is is noisy, inexpensive.

                   

II-Daisy-Wheel printer:- It produces quality type paper. It is a serial printer. Its a daisy while printer, because its look like a daisy. the daisy wheel is a disk made of plastic on which characters stand out in relief along the outer edge. A hammer strikes a Petal containing a character against the ribbon. It cannot print graphics. It can print 20 to 50 characters per second(cps). But there is also the drawback that is also noisy and slow.

                           

III-Drum printer:- It consist of a solid , cylindrical drum which is a complete set of character for each print position on a line is a continuously rotating drum behind and inked ribbon. Mean the number of print positions across the drum equals the number available on the page.  The Drum rotate at rapid speed. The speed of drum printer from 300 to above 2000 lines per minutes (lpm).

   

IV-Chain Printer:- It is a character printer. It is also called as band printer.  It is a chain of print character. there is one hammer for each print position. The print element in a chain printer is a metallic band that rotates horizontally in front of paper. the hammer strikes the page, pressing the paper against a ribbon and the character located at desired print location. There are mainly five section, each section consist of 48 character. It can produce 400 to above 2500 character per second.

V-Line Printer:- It is a high speed printer that can print a line at one time.  In companies or for business where large amount of work done through printer, there character at a time printers are very slow., so therefore there these type of printers are used ,  that can print a line at a time. it can typically print 1000 to 5000 lines per minutes. The major drawback is that it can not print graphics, print quality very low also very noisy .
       

Non- Impact Printer:-  The another is Non impact printers. non impact printers do not use a striking device to produce character on the paper. Now a days we use non impact printers. These are faster then the impact printers. There is no physical contact between the printing mechanism and the paper (mean no use of hammer for print a character). following are the examples of No impact printers are-

Ink jet printer, laser Printer etc.



I- laser Printers:- It also creates images with dots. however,  as in a photocopying machine, these images are created on a drum. Mean it works like a photocopy machine. laser printer produce images on paper by directing a laser beam at a mirror which bounces the beam onto a drum.
           laser printers use buffers that store an entire page at a time. There having built in RAM chips that use to store documents output from the computer. Some of the Laser Printers can print eight pages per minute. It is faster then other , it can print approximately 21, 000 lines per minutes or 450 pages per minutes.

       

II-Ink-Jet printers:- It works in same fashion of  Dot  matrix printers in the forms images or character with little dots. It can print in color and quieter then the laser printer. And also mush less expensive then the laser printer. However they are slower and print in a some what lower resolution like 400- 700 dot per inch. then laser printer. However, the dots are formed by tiny droplet of ink. Ink jet printers form chracters on paper by spraying ink from tiny nozzles through an electrical field that arranges the charged ink particles into characters at the rate of approximately 300 characters per seconds.

     

BLOCK DIAGRAM OF COMPUTER

Functional units of PC: 

-Control unit                         -  Arithmetic & logic unit(ALU)

- Main Memory unit             - Input unit

-output unit                           - Secondary storage.

1. Control Unit: This is the one of the central part of personal computer, which mainly control the operation. Its purpose to handle the processor control signal. It control the all the input and output flow in the computer system. basically it provide the communication between the input and output devices in computer system. It interpret the data or the information and send them for the further processing. It guide the computer flow between different media in system.

2. Arithmetic & Logic unit (ALU): It perform the arithmetical and logical operation and send them for the further processing It is the one of the main part of the central processing unit.  ALU has direct access to the processor for input and output . In some cases ALU divided into two part, first one the arithmetic unit (AU) and another one is logical unit (LU). AU perform arithmetic operation and LU perform the logical operation.

3. Main memory unit: This is a temporary memory. Where the data can be accessed randomly at any time. It is a volatile memory i.e its contents are lost when computer system is powered off. RAM is a volatile memory or temporary memory. It is normally of two type one is static RAM and another is dynamic RAM.

For more info click on Computer Memory:

4. Input unit: Computer is a device that take the input and give the output. So input unit basically include that input devices which is used to give the input to the computer system. This mean main purpose is to put the information in system by these devices. Input devices are like keyboard, mouse , scanner etc. There are various input devices that are discuss in the following links.

For more info click on the Input devices

5. Output unit: When any of the data or information sent by the system to any of the internal and external devices is a output. It include the devices like printer, speaker, desktop etc. for more discussion go and check the following link.
For more info click on Output devices

6. Secondary storage : Secondary storage mean permanent. Where we can permanent sore the data. It is non volatile memory. That mean contents are not erased or lost even your computer system is powered off.  There are another permanent storage like pen derive, CD, DVD etc are the some of the storage media where we can store the data for future use.

For more info click on Computer memory

Output devices

1-Monitor- It is also known as video display terminal or unit. It is an thin film transistor liquid crystal display (TFT-LCD). It is an output device It forms pictures from tiny dots that are called pixels that are managed in a rectangular form. The clarity of any picture or image depend upon the number of pixels. Computer monitor come in a variety of sizes. But important is your resolution.

2- Printer- This is the another important printer device. From printer we got the hard copy. It is basically accept text and graphics output from a computer system and transfers them on to the the paper that is called hard copy. There are two type of printers Impact and Non- Impact printer.  The main printer qualities are color, resolution, speed, memory . There is a figure that shows the laser jet printer.

for more information, go for the link
http://principleofcomputerprogramming.blogspot.in/2014/10/printers.html

3- Speaker- It is a hardware device that is connected to the sound card and provide us a sound as a output,which is generated by the computer system.  The main purpose of speaker is to produce audio output that can be heard by the listener. Speakers are transducers that coverts electromagnetic waves into sound waves.  It receive audio input from a device, that is either in analog or in digital.

4- Projector- It is another output device. It is an image projector. It help us for making presentation. That help us to make sure everyone in the room can view that presentation.

Input devices

1-Keyboard :- The most common and popular device is a Keyboard. That contain all the alphanumeric and symbol keys. It allows the user to enter the letter, numbers and symbols into the computer,  basically this keyboard help the user for inputting the data into the computer system. Keyboard is basically of two size 84 keys or 102 keys, but now a days 104 keys or 108 keys is available.

There are basically a five types of keys in there in keyboard-
I- Function keys:- There are f1 to f12 are 12 functions keys are present on the keyboard.these are the short keys. These are arranged on the top of the keyboard. Each keys has its own individual function.

II- Control key:- These includes Home, End, Insert, Page up,Page down,  Delete, Ctrl, Alt, Esc. These provide cursor and screen control. There are also four arrows keys.

III- Special purpose keys:- It include Shift, Caps lock, Num Lock, Space bar, Tab, etc.

IV- Typing keys- These include the letter keys  A to Z and digits keys 0-9 which generally look like a typewriter.

V- Numeric Keypad- It consist of 17 keys that are used for some calculation like arithmetic operation. These are basically to put the numeric data.


2- Mouse:- The another popular input device is a mouse. This is a pointing device. This is basically used for control the movement of cursor on the display or on the screen. There are mainly three types of mouse.
-Mechanical mouse.
-Opto-mechanical mouse.
- Optical mouse.

The first mouse used in the market is a mechanical mouse. In the mechanical mouse there is two click right and left and there is no scroll bar. After that there optomechanical mouse comes in market with a scroll bar in between the left and right click. After that at last now a days we used the optical mouse.In this optical mouse we used the laser light , there is a grid in the center part of mouse with a sensor there, that sense the laser light which move the cursor movement on the screen.The fig shows the optical mouse.

3- Light pen- This is another pointing device. It is used to select any of the picture or menu items on the display  or monitor screen. It consist of photocell and optical system placed in a small tube.Light pen can work with an CRT based display but not with LCD's and other display technology.

4- Track ball- This is another input device that is mostly used to move the pointer by moving the ball direction. It is like a mouse, there are also three buttons are there along with the ball.

5- Joystick-  This is another input device. It is consist of a stick which is pivot on the base and move its angle   or direction to the device which is controlling. Basically there is lever that move the direction of a pointer on the monitor screen. Pointer move according the movement of the joystick. These are normally used for computer games. Its like a mouse, the difference is when mouse stop moving the cursor on the screen stop moving but in this case the pointer continuing moving in the direction in which pointer is moving.

6- Scanner- This is a input device which is mainly used for scanning the  documents mean it work more then a photocopy machine. It is basically scan your hard copy and make a soft copy on your system, and transfer it to the hard disk for further manipulation. In this when any document is scanned, it is converted into digital form that is called a soft copy which can be editable. Scanner is used in many ways-
- Flatbed scanner.
- Sheet fed scanner.
- Handheld Scanner.
- Drum Scanner.

7- Graphic tab- It is another input device. This is used as a drawing tab, in which is used by the user to draw a picture, animation and graphics. It is used like user draw a image on paper using pencil. Today's some tab are also used to capture the data or signature.

8- Microphone- Microphone is a peripheral that allows computer user to input audio into the system. There is fig which show how microphone look like. It is basically used for Online chatting, voice recognition, adding sound to a multimedia presentation or for mixing music.
   

9- Optical mark reader- It is a special type of optical scanner that gather information by using a hardware device that detect a reflection and the type of mark made by pen or pencil from a card or from a piece of paper.Basically it scan printed form and reads predefined position and records where marks are made on the form.  

       

10- Optical character reader- It read text from paper  or take a photograph of that one and convert them into that in which computer can understand.

11-Bar code reader- It is a device for reading bar coded data which are in the dark line. there is fig that show the bar code reader. That mainly give the detail about the product like price etc.

12- Magnetic ink card reader - MICR is a font capable of recognition using magnetically charged ink. That are basically used in banks because there are large number of cheques to be processed everyday.This is enable them to process something 300 cheques per minute with 100% accuracy.. There at the bottom of every cheque there are a series of number which records the cheque number, customer's account number etc.
 

Difference between Input and output devices.

                                                              Computer input and output devices are the peripheral devices. First we have to discuss what is basically the input and output. Whenever any of the data and information give to the computer is a input and whenever some information and data sent by the system to any of the internal and external devices is a Output. A Input and output is normally used as a verb whether to give some input by the user to the system and take the output on the display or in the form of hard copy through printer.

An input devices converts incoming data and information into a pattern binary codes that is comprehensible for digital computer but output devices  reverse the process, convert the digital signal to make them user understandable.

Input devices are Keyboard, Mouse, Lighten pen, Track ball, Joystick, Scanner, Graphic tab, Microphone, Optical mark reader, Optical character reader, Bar code reader, Magnetic ink card reader etc.
For more information find link http://principleofcomputerprogramming.blogspot.in/2014/09/input-devices.html


Output devices are Monitor, printer, Speaker, Projector, plotter etc.

 For more information about output devices click on  http://principleofcomputerprogramming.blogspot.in/2014/09/output-devices.html