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Q1. a) What are the two criteria for classification of the advanced operating systems? Discuss any two operating systems in both the categories.

Answer : -

Advanced Operating Systems

  1. Architecture Driven System

    1. Network Operating System
    2. Distributed Operating System
    3. Multiprocessor Operating System

  2. Application Driven System

    1. Database Operating System
    2. Real-Time Operating System
    3. Multimedia Operating System

Network Operating System

A network operating system is a specialized operating system for a network device such as a router, switch or firewall.

Historically operating systems with networking capabilities were described as network operating system, because they allowed personal computers (PCs) to participate in computer networks and shared file and printer access within a local area network (LAN).

Network operating systems can be embedded in a router or hardware firewall that operates the functions in the network layer (layer 3).

Some important Network OS are listed below -


Distributed Operating System

A Distributed Operating System is an operating system that runs on a network of computers.

In a Distributed Operating System, each user thinks that running on a single large system with one operating system. The users don’t need to know where the files in the network.



Real-Time Operating System

Real time system means that the system is subjected to real time, i.e., response should be guaranteed within a specified timing constraint or system should meet the specified deadline. For example: missile systems, air traffic control systems, robots etc.

There are two types of Real-Time Operating System -

Q1. b) Discuss the key characteristics of modern operating systems.

Answer : -

Multi-threading - Multithreading is the ability of a program or an operating system process to manage its use by more than one user at a time and to even manage multiple requests by the same user without having to have multiple copies of the programming running in the computer. The process is divided into threads that can run simultaneously.

Symmetric Multi-processing - In Symmetric Multi-processing system a computer has more than one processor. These processors can share the same memory, data path, I/O facilities and also the same job for execution.

Advantages of Symmetric Multiprocessing -

Distributed Operating System - A Distributed Operating System is an operating system that runs on a network of computers. The operating system, memory files shared by the number of users in the network from the server. In a Distributed Operating System, each user thinks that running on a single large system with one operating system. The users don’t need to know where the files in the network.

Micro-Kernel Architecture - Kernel is the core part of an operating system which manages system resources. It also acts like a bridge between application and hardware of the computer. It is one of the first programs loaded on start-up (after the Bootloader).

A Micro-Kernel is the minimum software that is required to correctly implement an operating system. This includes memory management, process scheduling mechanisms and basic inter-process communication.

Object-Oriented Design - It is used for adding modular extensions to a small kernel. It also enables programmers to customize an operating system without disrupting system integrity.

Q2. Discuss the objectives and primary functions of the following connecting devices :

Answer : -


If multiple incoming connections need to be connected with multiple outgoing connections, then a hub is required. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. Hubs are multi-port repeaters, and as such they obey the same rules as repeaters. They operate at the OSI Model Physical Layer. Hubs are used to provide a physical Star Topology.


In an environment consisting of several network segments with different protocols and architecture, a bridge may not be adequate for ensuring fast communication among all of the segments. A complex network needs a device which not only knows the address of each segment, but also can determine the best path for sending data and filtering broadcast traffic to the local segment. Such a device is called a Router. Routers are both hardware and software devices. Router operates at the Network Layer of the OSI Model.

Q3. Explain virtual to physical address mapping concepts with the help of an abstract model.

Answer : - Your computer has two types of memory, Random Access Memory (RAM) and Virtual Memory. All programs use RAM, but when there isn't enough RAM for the program you're trying to run, Windows temporarily moves information that would normally be stored in RAM to a file on your hard disk called a Paging File. The amount of information temporarily stored in a paging file is also referred to as virtual memory. Using virtual memory, in other words, moving information to and from the paging file, frees up enough RAM for programs to run correctly.

A virtual address does not represent the actual physical location of an object in memory; instead, the system maintains a page table for each process, which is an internal data structure used to translate virtual addresses into their corresponding physical addresses. Each time a thread references an address, the system translates the virtual address to a physical address.

In this model, both virtual and physical memory are divided up into handy sized chunks called pages. These pages are all the same size. Each of these pages is given a unique number; the Page Frame Number (PFN). For every instruction in a program, for example to load a register with the contents of a location in memory, the CPU performs a mapping from a virtual address to a physical one. Also, if the instruction itself references memory then a translation is performed for that reference.

The address translation between virtual and physical memory is done by the CPU using page tables which contain all the information that the CPU needs. Typically there is a page table for every process in the system. Above figure shows a simple mapping between virtual addresses and physical addresses using page tables for Process X and Process Y. This shows that Process X’s virtual PFN 0 is mapped into memory in physical PFN 3 and that Process Y’s virtual PFN 2 is mapped into physical PFN 5. Each entry in the theoretical page table contains the following information :

Q4. Describe important Linux directories and files.

Answer : -

  1. / – Root

    • Every single file and directory starts from the root directory.
    • Only root user has write privilege under this directory.
    • Please note that /root is root user’s home directory, which is not same as /.

  2. /bin – User Binaries

    • Contains binary executables.
    • Common linux commands you need to use in single-user modes are located under this directory.
    • Commands used by all the users of the system are located here. For example : ls, ping, grep, cp, etc.

  3. /boot – Boot Loader Files

    • Contains boot loader related files.
    • Kernel initrd, vmlinux, grub files are located under /boot. For example : initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic.

  4. /dev – Device Files

    • Contains device files.
    • These include terminal devices, usb, or any device attached to the system. For example: /dev/tty1, /dev/usbmon0, etc.

  5. /etc – Configuration Files

    • Contains configuration files required by all programs.
    • This also contains startup and shutdown shell scripts used to start/stop individual programs. For example: /etc/resolv.conf, /etc/logrotate.conf, etc.

  6. /home – Home Directories

    • Home directories for all users to store their personal files. For example: /home/debabrata, /home/amit, etc.

  7. /lib – System Libraries

    • Contains library files that supports the binaries located under /bin and /sbin
    • Library filenames are either ld* or lib*.so.*, for example:,, etc.

  8. /media – Removable Media Devices

    • Temporary mount directory for removable devices. For examples, /media/cdrom for CD-ROM, /media/floppy for floppy drives, /media/cdrecorder for CD writer, etc.

  9. /mnt – Mount Directory

    • Temporary mount directory where sysadmins can mount filesystems.

  10. /opt – Optional add-on Applications

    • opt stands for optional.
    • Contains add-on applications from individual vendors.
    • add-on applications should be installed under either /opt/ or /opt/ sub-directory.

  11. /proc

    • Contains information about system process.
    • This is a pseudo filesystem contains information about running process. For example : /proc/{pid} directory contains information about the process with that particular pid.
    • This is a virtual filesystem with text information about system resources. For example : /proc/uptime

  12. /sbin – System Binaries

    • Just like /bin, /sbin also contains binary executables.
    • Linux commands located under this directory are used typically by system aministrator, for system maintenance purpose. For example : reboot, fdisk, ifconfig, etc.

  13. /srv – Service Data

    • srv stands for service.
    • Contains server specific services related data. For example, /srv/cvs contains CVS related data.

  14. /tmp – Temporary Files

    • Directory that contains temporary files created by system and users.
    • Files under this directory are deleted when system is rebooted.

  15. /usr – User Programs

    • Contains binaries, libraries, documentation, and source-code for second level programs.
    • /usr/bin contains binary files for user programs. If you can’t find a user binary under /bin, look under /usr/bin. For example : at, awk, less, etc.
    • /usr/sbin contains binary files for system administrators. If you can’t find a system binary under /sbin, look under /usr/sbin. For example: sshd, useradd, userdel, etc.
    • /usr/lib contains libraries for /usr/bin and /usr/sbin
    • /usr/local contains users programs that you install from source. For example, when you install apache from source, it goes under /usr/local/apache2
    • /usr/src holds the Linux kernel sources, header-files and documentation.

  16. /var – Variable Files

    • Content of the files that are expected to grow can be found under this directory.
    • This includes — system log files (/var/log); packages and database files (/var/lib), emails (/var/mail); print queues (/var/spool), lock files (/var/lock), temp files needed across reboots (/var/tmp), etc.

Q5. a) What will be the output of followings?

Answer : - Consider that the "myfile.text" contains the following lines -

Hard Disk
DVD Writer
Graphic Card
Hard Disk
mohan play football

$ cat myfile.text | head -7 | tail -5

Answer : - Print the last 5 lines from the first 7 lines of the "myfile.text" file

root@UBUNTU-PC:/MyDirectory# cat myfile.text | head -7 | tail -5
Hard Disk
DVD Writer
Graphic Card

$ cat filename | more ls -l > temp

Answer : -

$ sort myfile.text | unique

Answer : - Wrong Command

Right command is - sort myfile.text | uniq
First sort the file contents alphabetically, then remove the duplicate lines.

root@UBUNTU-PC:/MyDirectory# sort myfile.text | uniq
DVD Writer
Graphic Card
Hard Disk
mohan play football

$ cat myfile.text | grep “mohan” | wc -l

Answer : - Count the number of lines present in the "myfile.text" file which contains the particular pattern "mohan".

root@UBUNTU-PC:/MyDirectory# cat myfile.text | grep “mohan” | wc -l

$ ls -l | grep “jan”

Answer : - Display the detailed list of all the files and directories which name is contain the pattern "jan"

$ ls -l | grep | sort

Answer : -

Q5. b) What options can be used with grep command?

Answer : - Solve it Yourself

Q6. Briefly describe the features of followings and how are they configured in Linux?

Answer : -

(i) Apache Web Server

Apache is the most widely used Web Server application in UNIX-like operating systems but can be used on almost all platforms such as Windows, OS X, etc.

The reasons behind its popularity are :

(ii) DNS

Domain Name System is an Internet service that translates domain names into IP addresses. Since domain names are alphabetic, they are easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name might translate to

A domain name is divided into three part -

(iii) NFS Server

A network file system (NFS) is a type of file system mechanism that enables the storage and retrieval of data from multiple disks and directories across a shared network. It enables local users to access remote data and files in the same way they are accessed locally. NFS was initially developed by Sun Microsystems.

Q7. What are the purposes of dynamic addressing and directory services in Windows 2000? How are they configured?

Answer : - Solve it Yourself

Q8. What is the purpose of VPN and name VPN technologies supported by Windows 2000?

Answer : - A virtual private network, or VPN, is an encrypted connection over the Internet from a device to a network. The encrypted connection helps ensure that sensitive data is safely transmitted. It prevents unauthorized people from eavesdropping on the traffic and allows the user to conduct work remotely. VPN technology is widely used in corporate environments.

A VPN extends a corporate network through encrypted connections made over the Internet. Because the traffic is encrypted between the device and the network, traffic remains private as it travels. An employee can work outside the office and still securely connect to the corporate network. Even smartphones and tablets can connect through a VPN.

Types of VPNs

Virtual Private Network Protocols

Q9. What are Intrusion Detection Systems(IDS)? What IDS can do?

Answer : - An Intrusion Detection System (IDS) is a type of security software designed to automatically alert administrators when someone or something is trying to compromise information system through malicious activities or through security policy violations.

IDS is basically classified into two types :

Detection Method of IDS -

Q10. Elaborate the primary aspects of firewall? What are the limitations of firewall?

Answer : - A firewall is a network security system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented as both hardware and software, or a combination of both. Network firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

Firewalls can be either hardware or software but the ideal configuration will consist of both. In addition to limiting access to your computer and network, a firewall is also useful for allowing remote access to a private network through secure authentication certificates and logins.

Firewall Filtering Techniques

Firewalls are used to protect both home and corporate networks. A typical firewall program or hardware device filters all information coming through the Internet to your network or computer system. There are several types of firewall techniques that will prevent potentially harmful information from getting through :

In practice, many firewalls use two or more of these techniques in concert. A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.

Limitations of Firewall

Q11. How does RAID support fault tolerance systems? How is it implemented in Windows 2000?

Answer : - Fault-tolerance is the ability to survive of one or several disk failures.

RAID is a technology that is used to increase the performance and/or reliability of data storage. RAID stands for Redundant Array of Independent Disks. A RAID system consists of two or more drives working in parallel. There are different RAID levels, each optimized for a specific situation.

RAID 0 – striping

In a RAID 0 system data are split up into blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, this offers superior I/O performance. This performance can be enhanced further by using multiple controllers, ideally one controller per disk.



RAID 1 – mirroring

Data are stored twice by writing them to both the data drive (or set of data drives) and a mirror drive (or set of mirror drives). If a drive fails, the controller uses either the data drive or the mirror drive for data recovery and continues operation. You need at least 2 drives for a RAID 1 array.



RAID 5 – striping with parity

RAID 5 is the most common secure RAID level. It requires at least 3 drives but can work with up to 16 drives. Data blocks are striped across the drives and on one drive a parity checksum of all the block data is written. The parity data are not written to a fixed drive, they are spread across all drives. Using the parity data, the computer can recalculate the data of one of the other data blocks, should those data no longer be available. That means a RAID 5 array can withstand a single drive failure without losing data or access to data.



RAID 6 – striping with double parity

RAID 6 is like RAID 5, but the parity data are written to two drives. That means it requires at least 4 drives and can withstand 2 drives dying simultaneously. The chances that two drives break down at exactly the same moment are of course very small. However, if a drive in a RAID 5 systems dies and is replaced by a new drive, it takes hours or even more than a day to rebuild the swapped drive. If another drive dies during that time, you still lose all of your data. With RAID 6, the RAID array will even survive that second failure.



RAID 10 – combining mirroring and striping

It is possible to combine the advantages (and disadvantages) of RAID 0 and RAID 1 in one single system. This is a nested or hybrid RAID configuration. It provides security by mirroring all data on secondary drives while using striping across each set of drives to speed up data transfers.



Q12. List the different types of malicious code and compare the virus protection tools.

Answer : - Malicious software is any software that the user did not authorize to be loaded or software that collects data about a user without their permission.

Different Types of Malicious Software

Q13. What is Kerberos? Describe Kerberos management in Windows operating system.

Answer : - Kerberos is a ticketing-based authentication system, based on the use of symmetric keys. Kerberos uses tickets to provide authentication to resources instead of passwords. This eliminates the threat of password stealing via network sniffing. One of the biggest benefits of Kerberos is its ability to provide single sign-on (SSO). Once you log into your Kerberos environment, you will be automatically logged into other applications in the environment.

To help provide a secure environment, Kerberos makes use of Mutual Authentication. In Mutual Authentication, both the server and the client must be authenticated. The client knows that the server can be trusted, and the server knows that the client can be trusted. This authentication helps prevent man-in-the-middle attacks and spoofing. Kerberos is also time sensitive. The tickets in a Kerberos environment must be renewed periodically or they will expire.

When a user needs to access a service protected by Kerberos, the Kerberos protocol process can be divided into two phases - User Identity Authentication and Service Access.

User Identity Authentication - User authentication is a process of checking validity of identity information provided by users in the Kerberos authentication service. Identity information can be user names and passwords or information that can provide real identities in other forms. If user information passes the validity check, the Kerberos authentication service returns a valid Ticket-Granting Ticket (TGT) token, proving that the user has passed identity authentication. The user uses the TGT in the subsequent Service Access process.

Service Access - When the user needs to access a service, the user requests the Ticket-Granting Service (TGS) from the Kerberos server based on the TGT obtained in the first phase, providing the name of the service to be accessed. TGS checks the TGT and information about the service to be accessed. After the information passes the check, TGS returns a Service-Granting Ticket (SGT) token to the user. The user requests the component service based on the SGT and related user authentication information. The component service decrypts the SGT information in a symmetrical way and finishes user authentication. If the user passes the authentication process, the user can successfully access related resources of the service.

Kerberos in Windows Systems

Kerberos is very prevalent in the Windows environment. In fact, Windows 2000 and later use Kerberos as the default method of authentication. When you install your Active Directory domain, the domain controller is also the Key Distribution Center. In order to use Kerberos in a Windows environment, your client system must be a part of the Windows domain. Kerberos is used when accessing file servers, Web servers, and other network resources. When you attempt to access a Web server, Windows will try to sign you in using Kerberos. If Kerberos authentication does not work, then the system will fall back to NTLM authentication.

Q14. Define IPSec? What are its features? Discuss its implementation in Windows 2000.

Answer : - Exchanging sensitive information across a network, especially a public network, requires a security method that will protect the data in transit. That’s where Internet Protocol Security (IPSec) comes in. IPSec is a set of protocols that allows you to sign and encrypt data to be sent across an IP network, and authenticate and decrypt the protected packets on the receiving end. Windows 2000 Professional and Server include IPSec.

What is IPSec ?

IPSec is a set of protocols and cryptography-based services that work together to protect data from unauthorized access or tampering when it is sent across an IP network. IPSec provides three basic services :

Implementation of IPSec in Windows 2000

Windows 2000’s implementation of IPSec provides a high level of security, using a combination of algorithms and keys to encrypt the data so that it will be unreadable if intercepted along its route. IPSec uses two protocols to accomplish these tasks :

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