INFORMATION TECHNOLOGY UNIT II - NOTES

UNIT - II

OPERATING SYSTEM

OPERATING SYSTEM: An Operating System(OS) is the most important software that runs on a computer. An Operating System is a system software that acts as a interface between the user and the computer hardware. It manages the computers memory, process, and all of its software and hardware. It also allows you to communicate with the computer hardware. It is impossible to run the computer without an OS.

     The purpose of an OS is to provide an environment in which a user can execute programs in a convenient and efficient manner. It helps in booting up a computer system and running other applications. 

Functions of Operating System: 

File Management: It keeps the track of information, location, status and uses of file system. A file system is normally organized into directories for easy navigation and usage.

Device management: OS manages device communication via their respective drivers. OS does the following activities for device management. Keeps tracks of all devices. Programs responsible for this task is known as the I/O controller.

Processor Management: In multi-programming environment, OS decides which process gets the processor when and how much time. This function is called process scheduling. OS does the following activities for processor management. Keeps tracks of processor and status of process.

Memory Management:  It refers to management of Primary memory and Main memory. OS keeps the track of what part of primary memory are in use by whom.  Also it shows allocation of main memory and other storage areas to the system programs as well a suser programs.

Input/Output Management: It means assignment of the different input and output devices to one or more programs, while they are being executed.

Providing user interface: Each icon on a desktop represents code linking to the spot in which the icon represents which helps users to understand very easily. Also it works as a interface between computer's hardware and software.



Types of Operating System:

1. Batch Operating System: In batch operating system, the computer processess the instructions batch-wise. To speed up processing, jobs with similar needs are batched together and run as a group.

     Example: Payroll System, Bank Statement.

2. Single User Operating System: This type of OS is designed to be used by a single user to perform a single task. 

Example: Ms-Dos

3. Multi User Operating System:This type of OS is designed to be used by more than one user. 

Example: Unix, Linux

4. Multiprocessing Operating System: Multiprocessing system uses two or more procesors linked together to perform work simultaneously with short period of time.

5. Multi programming Operating System: In this type of operating system, we can operate many programs at one time. 

Example: Windows

BOOTING PROCESS:

Operation which is performed automatically by the computer is called as Booting Process. It is a start up sequence that starts the Operating System of a computer when it is turned on. During Booting process the computer will perform a self-diagnostic test called as POST and load necessary drivers and programs that help the computer and devices communicate.

TYPES OF BOOTING:

1. Cold Boot: When computer is turned off and turned on by using power button is cold boot.
2. Warm Boot: When computer is running and restarted is Warm Boost.

DISK OPERATING SYSTEM(DOS)

MS-DOS is a non-graphical command line operating system. It is derived from 86-DOS that was created for IBM compatible computers. It is written by Tim Paterson, and introduced by Microsoft in August 1981. MS-DOS allows the user to navigate, open and manipulate files on computer from command line.

Features of DOS:

1. Single user Operating System

2. It is based on Character User Interface(CUI)

3. It is Non-Graphical command line operating system.

Dos Commands:

A. Internal Commands: These commands are stored in the system memory and loaded fromt he Command.com. Internal commands are so-called because their instructions are a part of COMMAND.COM, the DOS command line interpreter. The internal commands are always in memory and can always be executed from any command line prompt.

List of Internal commands:

• MD(make directory): to create a new directory or sub directory.
• Synt: C:\MD <name> eg: c:\md snvmv
• CD(change directory): to move from one directory to another. 
• Synt: c:\cd\<name> eg: c:\cd snvmv
• RD(remove directory): it is used to remove an empty directory.
• Synt:c\rd <name> eg: c:\rd snvmv
• COPY CON: used to create a file.
• Synt:  copy con <file name> eg: c:\copy con <bcom>
• DEL: used to delete files.
• Synt: del <filename> eg: c:\del <bcom>
• TYPE: used to view the contents of text file
• Synt: type <file name> eg: c:\type bcom
• COPY: used to copy a file.
• Synt: copy <source filene > <destination file name> eg: c:\copy bcom bsc
• REN: used to rename the file
• Synt: ren<old filename><new filename> eg: c:\ren bsc bcom
• DIR: used to display the list of directories and sub directories
• Synt: dir
• CLS: used to clear the screen
• Synt: cls
• TIME: used to display current time and allows to change the time
• DATE: used to displays and change the current date
• VER: used to displays the current DOS version

B. External Commands: These commands require certain special DOS files to get executed. These commands reside in secondary memory and whenever the OS require them they are loaded into primary memory.

• FORMAT: used to prepare a disk for use by DOS
• eg: format c:
• CHKDSK: used to analyze the disk and display the memory status report
• eg: chkdsk c:
• DISKCOPY: used to make an exact copy of diskette, including hidden system files if they ar e present
• eg: diskcopy c: d:
• TREE: this command will graphically displays the directory structure of a drive or path
• eg: tree c:
• LABEL: this command allows user to assign, change or remove a volume label on a disk
• eg: label d:
• MEM: this command is used to display the amount of used and free memory.
• eg: mem
• SORT: used to read the input, sort the data and then write the sorted data on to scree or file.
• eg: sort
• RESTORE: used to restore all files which are backed up using back up command.
• eg: restore c: d:
• DISKCOMP: used to compare the contents of the disk in the source drive to the target drive.
• eg: diskcomp c: d:
• BACKUP: used to make backup copies of the file
• eg: backup c: d:

WILD CARD CHARACTERS:

      Wild cards are the symbols that are used to replace or represent one or more characters. There are two wild card characters in DOS. They are:
a.    ASTERICK(*) - represents one or more characters
        eg: dir *.doc
b.   QUESTION MARK(?) - Represents a single character
         eg: dir a?mp

COMPUTER VIRUS AND ANTI-VIRUS SOFTWARE:

It is small computerprogram that affects the computer. A virus is a executable file. It is loaded on a system without our knowledge and becomes active when user executes the program that contains the virus.
     Some computer viruses are programmed to harm the system by damaging programs and deleting files and some may crash the system completely.
     Virus can be enter by using floppy , transferring file like images and music files, downloading files or softwares, visiting infected web sites etc.
      Antivirus software is a type of software that is used for scanning and removing viruses from a computers. It is a program or set of program that are designed to prevent, search fro detect, and remove software viruses, and other malicious software like worms, trojans, adware and malwares more.
      There are several different companies that build and offer anti-virus software like:
Kasperkey, Quickheal, Nortan, Avast, AVG etc.
     
 Types of Computer virus   :

1. Boot Sector virus: Boot sector is the most important part which containg information about the disk and the program to start computer from the disk. Boot sector virus affects the boot sector.
2. File Infector virus: A virus that live within a file, typically a.exe file. Whenthefile is executed it will run its nasty code.
3. Polymorphic virus: It is a virus written to change itself in order to avoid virus detection.
4. Macro virus: Macro virus is a virus that hides itslf inside macros used by program such as microsoft excel.
5. Time bomb: It is a virus written to execute at a later date or upon an action performed.

HACKERS

    Hackers are people who try to gain un-authorized access to you computer. This is done through the use of 'backdoor' program installed on your machine. Computer can be protected from these hackers by using a firewall or an anti virus. A hacker is a term that first started being used in the 1960s. It was used to described a programmer or someone who hacked computer code. Later the term evolved into a individual who had an advanced understanding of computers, networking, programming or hardware.

     Students, Thieves, Crashers, Criminals are the types of hackers.

CRYPTOLOGY AND CRYPTOGRAPHY

Cryptography: It is the study of both hiding information and of revealing hidden information. It has two aspects:  (a) Cryptography   (b) Cryptanalysis.

Cryptography is a technique of secret writing especially code method of storing and transmission data in a particular form so that only those for whom it is intended can read and process it. In short it is the process of hiding information.

Cryptanalysis:  is the study of breaking codes. The aim to reveal the hidden meaning even if the key of main algorithm is not available.

The main objectives of cryptography are:

• Confidentiality: To ensure that the information is not read by anyone for whom it was unintended and is read only by authorized parties,
• Integrity: To ensure that the information was not altered in storage or transit between sender andinternded receiver.
• Non-repudiation: To ensure that the sender of the information cannot deny at a later stage his or her intentions in the creation or transmission of the information.
• Authentication: To ensure that the sender and receiver can confirm each other identity and the origin/ destination of the information.