OPERATING SYSTEMS
by Shivajirao Jadhav , Mumbai
Marks: 10 (15)
Definition: An operating system (OS) is a program, which acts an interface between the user of computer and computer hardware.
An operating system (OS) is system software. It manages computer hardware and software resources and provides common services for computer programs.
Main functions of an operating system:
It boots the computer.
It performs basic computer tasks e.g. managing the various peripheral devices like keyboard, mouse, printer etc.
It makes the hardware convenient to use.
It helps users to execute the programs.
It provides security of information to users.
It provides a user interface like command line interface, graphical user interface.
Handles system resources such as computer's memory and sharing of the central processing unit (CPU) time
It performs error handling
Services in OS.
The operating system provides certain services to users. There are three major categories of services-
Information management (IM)
Process management (PM)
Memory management (MM)
Information management (IM):
It refers to set of services used for storing, retrieving, modifying or removing the information on various devices.
These system services manage the organization of information in terms of directories and files. It allocates and de-allocates the sectors to various files.
Some of system services provides under IM are-
Create a file
Create a directory
Open a file
Close a file
Read data from file to buffer
Write data from buffer to file
Move the file pointer
Read and return file’s status
Create a link
Change working directory
Memory Management (MM):
Memory management refers to management of Primary Memory or Main Memory.
When a program is to be executed, the OS loads the program in main memory.
The operating system keeps a list of free memory locations.
Before program is loaded in the memory from disk, the MM consults this free list, allocates the memory to process.
The OS keeps list of free memory locations.
The memory allocated to process depends on program size.
When program is executed completely, it removes from main memory and again modifies the list.
Processor Management (PM):
In multi user system operating system, a number of users located at different terminals run the same or different programs.
A computer has only one CPU and it can execute only one instruction belonging to any one of all these programs. In such case OS has to keep track of all running programs, called processes.
In multiprogramming environment, the OS decides which process gets the processor when and for how much time.
The services provided under process management are-
Read process
Block process
Terminate process
Resume process
Dispatch process
Suspend process
Delay process
Graphical User Interface (GUI):
The interface which replaces cryptic commands by their graphical representation are called Graphical User Interface (GUI). It allows the use of icons or other visual indicators to interact with electronic devices.
Windows operating system is GUI based operating system.
Advantages of GUI:
GUI operating systems are much easier to learn and use.
With GUI, commands are replaced by graphics. It is nor necessary to remember the commands.
With GUI, user can run several programs simultaneously.
User can communicate and exchange data between programs without transferring or copying files.
Windows:
In windows, different applications are shown on screen by icons. The screen is split into different partitions. Each partition can be of different size. User can run different applications in each partition of screen. Each of these partitions is called a window. User can open one or more applications at a time by clicking on windows.
Types of Operating Systems:
Linux:
Linux is rapidly evolving operating system. It is similar to UNIX system. It is also compatible with UNIX. In early days, Linux source code was available for free on internet. It is free to use. Its functionality list is quite similar to that of UNIX. It is free software. It is free in sense that people can copy it, modify it, use it in any manner they want.
Features of Linux:
Linux is multiuser operating system
It works on different types of hardware in same way.
Linux source code is freely available.
Linux is a multiprogramming system means multiple applications can run at same time.
It can run on machine having 4MB of RAM.
Linux presents standard interfaces to both the programmer and user.
Linux supports a wide base applications.
The file system in Linux obeys UNIX semantics.
Windows 7 Operating system:
Windows 7 operating system is proprietary softer owned by Microsoft Company.
Features:
High speed
User friendly
Multiuser and multitasking
Compatibility with Vista
Lower hardware required
High GUI interfaces
High security
Easy updations in programs
Supports multiple and new technologies
Touch enabled
Windows 8 Operating System:
The transition from Windows 7 to Windows 8 introduced a number of new features across various aspects of the operating system. These include a greater focus on optimizing the operating system for touch screen-based devices such as tablets.
Features:
Speedy boot time
Innovative and dynamic desktop
Improved search function
Compatible with touch screen displays
Windows store-user can purchase, download and install apps. The store will offer free and paid applications.
Multiple monitor support
Refresh and reset facility
Built in antivirus with windows defender
Access and Security Aspects of O.S.:
Definition:
The system that uses specific security features to access the information only by authorized individuals to read, write, create or delete is called security system.
The aspects/elements/ terms of security system are-
Confidentiality: Ensuring that the information is not accessed in an unauthorized manner, i.e. by controlling Read operations.
Integrity: Ensuring that the information is not amended or deleted in an unauthorized manner, i.e. by controlling write operations.
Availability: Ensuring that the information is available to authorized users at right time i.e. by controlling read and delete operations and ensuring fault recovery
.
Security threats:
Sharing and protection are requirements of any modern computing. More sharing gives rise to more possibility of security threats.
The major threats to security can be categorized as:
Tapping: Unauthorized use of service.
Disclosure: Unauthorized disclosure of information.
Amendment: Unauthorized alteration or deletion of information.
Fabrication: Unauthorized fabrication of information.
Denial: Denial of service to authorized users.
Tapping and discloses are passive threats and other are active threats.
In first two cases the information goes to third party without knowledge of other two parties.
In disclosure, source party willingly discloses information to the third party.
Attacks on Security:
The security system can be attacked in number of ways.
Authentication:
It means verification of access to system resources. Following are ways to in this regard-
Guessing or stealing somebody else’s password and then use it.
Use of vendor supplied password which can be used by only system administrator.
Finding password by trial and error method.
If user logs on and goes for tea, then intruder can use terminal
Writing dummy login program to the fool user.
Browsing:
In some systems, there exist files with accesses controls, which are permissive.
One can browse through the system files to get this information, after which unprotected files/data bases could be easily accessed.
Confidential information could be read or even modified.
Trap doors:
Sometime, software engineers leave some entry point to modify their programs.
These are called trap doors. They can be misused by others.
Invalid parameters:
Passing invalid parameters may cause serious security violations.
Line trapping:
A special terminal is used to tap into a communication line. It causes access to confidential data.
Electric data capture:
Use of active or passive wire-taps, or mechanism to pick up the screen radiation and to recognize what is displayed on screen, is called electronic data capture.
Waste recovery:
By using some technique, deleted files can be recovered. Passwords may be recollected. It is waste recovery.
Rouge software:
Certain programs like worms, viruses attacks on system.
Computer worms:
A computer worm is complete a program by itself.
It is written in such a way that it spreads to other computers over a network, but while doing this; it consumes the network resources to a very large extent. It can bring the network to halt.
Usually, worm does not harm any other program.
It just spreads, thereby consuming large resources such as transmission capacity, disk storage and denying services to others.
The worm gets a mailing list and using this it sends copy of itself to all those addresses.
The worm is harmful to organizations operating over a network.
The worm be protected by strong security and various check points in communication system.
Computer virus:
A computer virus is program segment written with a clear intention of infecting other programs.
It gets onto many useful programs.
Virus is not a complete program. It can not operate independently.
Virus causes direct harm to system. It can corrupt code and data.
There are several types of viruses:
Boot Sector Infectors
Memory Resident Infectors
File Specific Infectors
Command Processor Infectors.
General Purpose Infectors
Basis of classification:
Boot sector infectors: Virus can get into system memory if the machine is booted with an infected floppy or hard disk.
Memory Resident Infector: It loads upon execution of an infected file. Subsequently, whenever a non infected file is executed, the virus infects it
File specific Infectors: Infection occurs when an infected file is executed. The virus then load it’s at viral code into memory. In addition to infecting, the virus also reboots the system.
General purpose Infector: General purpose infector can infect exe file.
Command processor Infector: Infection occurs when infected file is executed. It infects com files as they are accessed.
Mode of Operation of virus:
Virus works in number of ways. Developer of virus is a bright person who knows the operating system.
Typically viruses are developed under MS-DOS.
Viruses spread with games, unauthorized software and they are distributed to people free of charge.
Virus detection:
Virus detection programs checks for integrity of binary files.
The program maintains a checksum on each file. A mismatch in it indicate virus.
Some program reside in memory and continuously monitor memory and I/O operation.
Virus removal:
For some viruses bit pattern code can be predicted.
The virus removal program scans disk for pattern of known viruses. On detection it removes them. The data recovery is impossible, if the virus has already damaged data.
A generalizes virus removal program is very difficult to imagine due to the multiplicity of the viruses and the creativity with which they are constructed.
Virus prevention:
Prevention is best measure as user cannot recover after virus infection.
The safest way is to buy official, legal copies of software from reliable sources.
Free, unreliable software should not be used.
Frequent back up and running of monitoring programs also helps prevention.
Difference between computer worm and computer virus:
Questions
Marks wise Questions: 1M(2), 3M(1), 4M(1), 6M(1)
1. Fill in the blanks with given alternatives.
Operating system is ------------.
(i) Hardware (ii) Software (iii) Input device (iv) Output device
Linux is -------- software
(i) Public domain (ii) Free (iii) Paid (iv) private
Windows 98 is ------------ operating system.
(i) Single user multitasking (ii) Multiuser (iii) Time sharing (iv) Muitithreading
-------- is not an operating system.
(i) UNIX (ii) LINUX (iii) MS-DOS (iv) C
----------- spreads more rapidly but causes less damage to computer networks
(i) Virus (ii) Worms (iii) Threat (iv) None
------- was first operating system used in computers.
(i) LINUX (ii) Windows 7 (iii) Windows 8 (iv) UNIX
2. State true or false.
Windows 7 is Microsoft operating system
Operating system is interface between computer user and computer hardware.
LINUX is UNIX base operating system.
3. Match the following.
A B
(1) UNIX (a) Operating system
(b) Operating system (b) Software
4. Answer the following.
What is an operating system of computer?
Write functions of operating system.
Write the names of services in operating system.
What is information management? Write its service calls.
What is memory management?
What are the services provides under processor management?
What is Graphical User Interface? Write its advantages.
Write the features of LINUX operating system.
Write the features of Windows 7 operating system.
Write the features of Windows 8 operating system.
Define Security regarding the operating system.
What are the different security aspects of operating system?
What are the major threats to security of computing system?
In what ways the security system can be attacked?
Write a note on computer worms.
What is computer virus? Write its types.
Explain mode of operation of computer virus.
Explain virus detection, removal and prevention.
Differentiate between computer worm and computer virus.
