class 12 computer note


System Development Concept


System is a set of interacting or interdependent components forming an integrated whole. A system can be described as a set of objects joined together for a common objective.

Components of system:

  1. Hardware: hardware refers to the physical layer of the information system. It includes computers, networks, scanners, digital capture devices, and other technology-based infrastructure.

  2. Software: software refers to the logical layer of information system that makes hardware function properly. It includes system software (OS, device driver, etc.) and application software.

  3. Data: data is raw facts, figures, and measurements, etc. which are used as input for the system. It may be alphabets, digits, figures and other symbols.

  4. Processes: processes, or procedures, describe the tasks that users, managers, and IT staff members perform.

  5. People: people refer to users who interact with information system. The users within the organization include mangers, technicians, sales representatives, corporate officers, etc. are called internal users and the users outside the organization include customers, suppliers, etc. are called external users.



Information System

An information system is a computer based system which is an integrated set of different components for collection, process, storage and transmission of data. Simply, it us a system which processes supplied/collected data and generates information that can be used for decision making at different levels for the betterment of an organization. The types of information system are:

  1. Transaction processing system: it processes data resulting from business transactions, updates operational database such as sales and inventory processing and accounting systems.

  2. Management information system: it is the integrated modern approach of management, information and computerized system. It provides information to support the operations, management, decision making functions of an organization.

  3. Decision support system: It is the information system at the organization's senior level management that combines data and sophisticated analytical models or data analysis tools to support semi-structures and unstructured decision makings.

  4. Executive support system: it is also known as executive information system. It operates on the executive level of management. It provides critical information from many sources customized to the information needs of executives.


System Analyst

System analyst is a people who is involved in analyzing, designing, implementing and evaluating computer based information to support the decision making and operation of an organization.

The roles of system analyst area as follows:

  1. Change event

  2. Investigator and event

  3. Architect

  4. Psychologist

  5. Motivator

  6. Defining and prioritizing the requirements

  7. Analysis and evaluation

  8. Designing system

The characteristics of system analyst are as follows:

  1. Knowledge of organizations

  2. Knowledge of computer system

  3. Good inter-personal relation

  4. Communication skills

  5. Analytical skill

  6. Breadth of knowledge


Waterfall model

it is a oldest type of model for software engineering. The fundamental processes of waterfall model are as follows:

  1. Requirements analysis and definition: it is the first stage of waterfall model. In this stage, the developer should identify the actual requirements of the given problem.

  2. System design: in this stage the systems design process partition the requirements to either hardware or software systems.

  3. Implementation and unit system: During this stage, the system design is realized and tested as a complete system to ensure that the software requirements have been met.

  4. Operation and maintenance: in this stage, the system is installed to the desire location. The maintenance involves correcting errors which were not discovered in earlier stages of the life cycle, improving the implementation of system units and enhancing the system's service as new requirements are discovered.


Prototyping model

It is the iterative process of system development which is more appropriate for developing new system where there is no clear idea of requirements, inputs and outputs.

  1. Identify the user needs: the system analyst interviews the user to obtain an idea of what is required from the system.

  2. Develop a prototype: the system analyst, working uses one or more prototyping tools to develop a prototype.

  3. Determine if prototype is acceptable: the analyst educates the user in prototype use and provides an opportunity from becoming familiar with the system.

  4. Use the prototype: the prototype becomes the operational system.


Spiral system

In this model, process is represented as a spiral rather than as a sequence of activities with backtracking.

  1. Planning: the project is reviewed and a decision made whether to continue with a further loop of the spiral. If it is decided to continue, plans are drawn up for the next phase of the project.

  2. Risk analysis: for each of the identified project risks, a detailed analysis is carried out. Steps are taken to reduce the risk. For example, if there is a risk that the requirements are inappropriate, a prototype system may be developed.

  3. Software development: after risk evaluation, a development model for the system is chosen.

  4. User evaluation: specific objectives for the phase of the project are defined by the evaluation of users. Constraints on the process and the product are identified. And a detailed management plan is drawn up.




It is the iterative process of system development which is more appropriate for developing new system where there is no clear idea of requirements, inputs and outputs.

Advantages of Prototyping

  1. Communications between the systems analyst and user are improved.

  2. The expert system can do a better job of determining the user's needs.

  3. The user plays a more active role in system development.

  4. The expert and the user spend less time and effort in developing the system.

  5. Implementation is much easier because the user knows what to expect.

  6. A system is developed through operational prototyping is capable of easy adaptation.

Disadvantages of Prototyping

  1. Because of the iterative nature of prototyping, there is no definite deliverable or competition deadline.

  2. Code inefficiencies may be a drawback in terms of functionality.

  3. The computer-human interface provided by certain prototyping tools may not reflect good design techniques.



SDLC consists of a set of development activities that have a prescribed order. It is the development of software in chronological order.

The different phases of SDLC are as follows:

  1. System study: A system is intended to meet the needs of an organization. Thus the first step in the design is to specify these needs or requirements. The top manager of the organization takes the basic decision to use a computer based (information) system for managing the organization.

  2. System analysis: system analysis is the dissection of a system into its component pieces to study how those component pieces interact and work. System analysis is a term that collectively describes the early phases of development. It is defined as those phases and activities that focus on the business problem, independent of technology.

  3. Feasibility study: feasibility study is the most important activity in the system analysis phase. It analyses the proposed system from different aspects so that it makes us clear that how practical or beneficial the system will be to the organization. So it tells us whether the system is feasible to design nor not.

  4. System design: the next step is to develop the logical design of the system. During this phase, the logic of the system, namely, the information requirement of users, and use this to find the necessary database.

  5. System development: after designing a logical diagram of a system then next step is to convert into program. This process is called system development. Flowchart, algorithm, Pseudocode, etc. are the outlines the procedures for taking the input data and processing it into usable output.

  6. System testing: it is an investigation conducted to provide stakeholders with information about the quality of the product or service under test. System testing also provides an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation.

  7. Implementation: implementation involves testing the installed system, converting from the old system to the new one and training the users. This phase consists of implementation of the system into a production environment, and resolution of the problem identified in testing phase.

  8. Maintenance and review: it begins after the system is implemented. Like any system, there is an ageing process that requires periodic maintenance of hardware and software. The content of the review will include objectives met, cost, performance, standards and recommendation.


Feasibility study

Feasibility study is the most important activity in the system analysis phase. It analyses the proposed system from different aspects so that it makes us clear that how practical or beneficial the system will be to the organization. So it tells us whether the system is feasible to design nor not. Thus it is necessary before system design.

The different levels of feasibility study are as:

  1. Economical feasibility: it concerns with cost effectiveness of the system. The main objective of economical feasibility is to calculate approximate cost-both the development cost and the operational cost and the benefits from the system.

  2. Technical feasibility: it concerns with the availability of the hardware, software and the support equipments for the complete development of the system.

  3. Operational feasibility: it concerns with smooth operation of the system. It is all about the problems that may occur during operation of the system after its development.

  4. Behavior feasibility: it concerns with behavior of the users and the society towards the new system. Generally, most of the traditional employees are not easily ready to upgrade them with the new system.

  5. Schedule feasibility: it is the process of splitting project into tasks and estimate time and resources required to complete each task. It determines the deadline to complete a system and schedule the task accordingly.

  6. Legal feasibility: it concerns with legal issue of the system. If the system is illegal then the system designing is meaningless. Everything is measured whether it is legal or illegal. It considers copyright law, foreign law, foreign trade, tax, etc.


System testing

It is an investigation conducted to provide stakeholders with information about the quality of the product or service under test. System testing also provides an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation.

  1. White box testing: white box testing of software is predicted on close examination of procedural details. Logical path through the software and collaborations between components are tested by providing test case that exercises specific sets of conditions or loops. It is used when the tester has access it the internal data structures and algorithms including the code that implement these.

  2. Black box testing: black box testing treats the software as a black box –without any knowledge of internal implementation. Black box testing methods include: equivalence partitioning, boundary value analysis, specification based testing, etc. it is also called functional testing because it tests whether a system is functioning or not.




System flowchart describes the internal architecture of a system that describes how data are moved inside the internal components of a system. Program flowchart describes to solve the application types of real world problem. The different symbols used in system flowchart are defined below:






DFD is the logical diagram to describe the flow of data inside the components of system. It is easier to understand or grasp when being explained and most important to all, it is much more precise and less ambiguous than a narrative one. The main components are: process, data store, data flow, external entities.


ER diagram

The E-R diagram is an overall logical structure of a database that can be expressed graphically. It was developed to facilitated database design and the simplicity and pictorial clarity of this diagramming technique have done great help in the designing part of database. The main components are attributes, entities and relationship.


Case diagram

computer aided software engineering tool is automatic computer based program that helps for software engineering and SDLC process. It us very fast and effective tools for the development of big scale software. It helps in analysis, design, implementation, testing and maintenance.



Unified Modelling Language is a standardized general purpose modelling language in the field of object-oriented software engineering. The standard is managed, and was created by, the object management group. UML includes a set of graphic notation techniques to create visual models of object-oriented software.


System flowchart

System flowchart describes the internal architecture of a system that describes how data are moved inside the internal components of a system. Program flowchart describes to solve the application types of real world problem.


Relational Database Management System (RDBMS)

The database system which stores and displays data in tabular format of rows and columns, like spreadsheet, is known as Relational Database Management System.


Different between Database and DBMS

Database: it is a collection of related information about a subject organized in a useful manner that provides a base or foundation for procedure, such as retrieving information, drawing conclusion and make decision.

DBMS: A DBMS is a set of programs that manages the database files. It allows accessing the files, updating the records and retrieving data as requested.

The technique for designing a database using top-down methods is to write a main database parts that names all the major storage and retrievals it will need. Later, the programming team looks at the requirements of each of those database components and the process is repeated.

The top-down method starts from the general and moves to the specific. Basically, you start with a general idea of what is needed for the system and then ask the end-users what data they need to store. The analyst will then work with the users to determine what data should be kept in the database. Using the top-down method requires that the analyst has a detailed understanding of the system. The top-down method also can have shortcomings. In some cases, top-down design can lead to unsatisfactory results because the analyst and end-users can miss something that is important and is necessary for the system.


Different database models

  1. HierarchicDal database model: this is one of the oldest type of database models. In this model data is represented in the form of records. Each record has multiple fields. All records are arranged in database as tree like structure. The relationship between the records is called parent child relationship in which any child record relates to only a single parent type record.

  2. Network database model: it replaced hierarchical network database model due to some limitations on the model. Suppose, if an employee relates to two departments, then the hierarchical database model cannot able to arrange records in proper place. So network, database model was emerged to arranged non-hierarchical database. The structure of database is more like graph rather than tree structure.

  3. Relational database model: in this model, the data is organized into tables which contain multiple rows ad columns. These tables are called relations. A row in a table represents a relationship among a set of values. Since a table is a collection of such relationships, it is generally referred to the mathematical term relation, from which the relational database model derives its name.

  4. Entity-Relationship database model: this model is based on perception of a real world that contains a collection of basic objects, called entities and of relationship among these objects and characteristics of an entity. It shows relationship between different entities.


Advantages of the database being centralized

  1. easier to organize, edit, update and back-up the data

  2. less data duplication - data is only entered once but can be accessed by many users

  3. data integrity - because data is stored once different data is no longer held in different databases in various departments around the organization


Advantages of database

  1. Sharing data

  2. Reduced data redundancy

  3. Data backup and recovery

  4. Inconsistency avoided

  5. Data integrity

  6. Data security

  7. Data independence

  8. Multiple user interfaces

  9. Process complex query


Domains and Tuples

In data management and database analysis, a data domain refers to all the values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values.

Tuple is the collection of information about the attributes of table for single instance. In simple this also can be called as a 'row' in a Table.



Different between centralize and distributed database system

Centralized database system

Distributed database system

Simple type

Complex type

Located on particular location

Located in many geographical locations.

Consists of only one server

Contains servers in several locations

Suitable for small organizations

Suitable for large organizations

Less chance of data lost

More chances of data hacking, lost

Maintenance is easy and security is high

Maintenance is not easy and security is low

Failure of system makes whole system down

Failure of one server does not make the whole system down

There is no feature of load balancing

There is feature of load balancing

Data traffic rate is high

Data traffic rate is low

Cost of centralized database system is low

Cost of distributed database system is high


DBA and responsibilities of DBA

DBA is the most responsible person in an organization with sound knowledge of DBMS. He/she is the overall administrator of the system. He/she has the maximum amount of privileges (permission to access the database) for accessing the database, settings up system and defining the role of the employees which use the system.

Responsibilities of DBA:

  1. DBA defines data security, schemas, forms, reports, relationships and user privileges.

  2. DBA has responsibility to install. Monitor and upgrade database server.

  3. DBA provides different facilities for data retrieving and making reports as required.

  4. DBA has responsibility to maintain database security, backup-recovery strategy, and documentation of data recovery.

  5. DBA supervises all the activities in the system: addition, modification and deletion data from the database.


State and different types of data integrity

Mainly there are 3 types of data integrity constraints used in the database system. They are as:

  1. Domain integrity constraints: it defines a set range of data values for given specific data field. And also determines whether null values are allowed or not in the data field.

  2. Entity integrity constraints: it specify that all rows in a table have a unique identifier, known as the primary key value and it never be null i.e. blank.

  3. Referential integrity constrains: it exists in a relationship between the two tables in a database. It ensures that the relationship between the primary keys in the master table and foreign key in child table are always maintained.


Normalization and normalization process

Normalization is a database design process in which complex database table is broken down into simple separate tables. It makes data model more flexible and easier to maintain. There are two goals of the normalization process: eliminating redundant data and ensuring data dependencies make sense.

For example: the table shown is our database without normalized. Here in table we can see that for the large records of this table, there would be multiple data row of same values especially in the country and city column. So, we can normalize the table by splitting it into two tables where one table only stores the location area of each person name and could be referenced by some unique id. Say Area code.





















The above table can be normalized in two tables as below:



Area code












Area code
















Data and information: Data is defined as the raw facts and figures. It could be any numbers, alphabets or any combination of it.

When data are processed using a database program or software, they are converted to the meaningful result, called information.


Field and record: A column in a table is called field and it contains specific piece of information within a record.

A row in a table is called record and it contains information about person, event, etc. Another name of record is tuple.


Data dictionary: A data dictionary is a file which contains meta-data that is data about data. It also called information system catalogue. It keeps all the data information about the database system such as location, size of the database, tables, records, fields, user information, recovery system, etc.


DDL: DDL is used by the database designers and programmers to specify the content and structure of the table. It is used to define the physical characteristics of records. It includes commands that manipulate the structure of objects such as views, tables, and indexes, etc.


DML: DML is related with manipulation of records such as retrieval, sorting, display and deletion of records of data. It helps user to use query and display reports of the table. So it provides technique for processing the database.


Primary key: the field or fields that contain the unique value can be set as primary key. It does not permit duplicate or null values.


Relationship: A relationship is an association among several entities and represents meaningful dependencies between them. It is represented by diamond. There are 3 types of relationship:

  1. One to one

  2. One to many

  3. Many to many


Communication and Networking

Computer Network

It is defined as the collection of two or more autonomous computers which are interconnected together for sharing resources with the help of transmission media and set of protocols.

Advantages of Computer Network

  1. Sharing resources: hardware resources such as processor, storage devices, printers, scanner, etc. can be shared among us using computer network. It helps to minimize the operational cost of an organization.

  2. Faster and cheaper communication: communication in modern days has become very faster and cheaper to send information to a long distance through network.

  3. Centralized control: all network resources such as computers, printer file , database , etc can be managed and controlled by a central connecting computer also known as the server.

  4. Backup and recovery: server is used to keep data as backup. It maintains backup of all individual computer’s information.

  5. Remote and mobile access: a remote user can access resources from the distance using computer network.

Disadvantages of Computer Network

  1. Expensive: In order to install computer network, we require some extra cost to purchase networking devices such as hubs, switch, cables, etc.

  2. Security problems: network security is the most challenging job for network administrator in order to protect network resources from authorized users and physical destructions.

  3. Needs technical person: it is very difficult to install and operate good computer network.


Types of Computer Network

On the basis of size computer networks can be classified into three categories:

  1. Local Area Network (LAN): A LAN is privately owned small size network. It spans only in small geographical area such as within a room, office, buildings or up to few kilometers (2 to 3 Km). it connects the network resources such as computers, faxes, printers and various networking devices.

  2. Metropolitan Area Network (MAN): A MAN can be either public or privately owned network. Its size is bigger than LAN and smaller than WAN. It spans within one metropolitan city or larger geographical area. It can connect large number of computers and heterogeneous multiple LANs within a city maximum, up to 100Km.

  3. Wide Area Network (WAN): A WAN is basically public type heterogeneous network. It is the largest sized network and connects millions of computers, thousands of LANs, hundreds of MANs around the countries, continents and even the whole world.


Difference  between LAN and WAN



LAN (Local Area Network) is a computer network covering a small geographic area, like a home, office, school, or group of buildings.

WAN (Wide Area Network) is a computer network that covers a broad area (e.g., any network whose communications links cross metropolitan, regional, or national boundaries over a long distance).

High speed (1000 mbps)

Less speed (150 mbps)

Network in an organization can be a LAN

Internet is a good example of a WAN

If there is a need to set-up a couple of extra devices on the network, it is not very expensive to do that.

For WANs since networks in remote areas have to be connected the set-up costs are higher. However WANs using public networks can be setup very cheaply using just software (VPN etc).

LAN covers 100 m

WAN covers more than 100 m

Experiences fewer data transmission errors

Experiences more data transmission errors as compared to LAN

Typically owned, controlled, and managed by a single person or organization.

WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management over long distances.



Network topology and it's types

Network topology refers to the physical layout of the network. It shows the geometrical representation of all links and linking devices, also called nodes. Its types are as:

  1. Bus topology: computers are connected to a single continuous cable that is called bus. A bus must be terminated on both sides to prevent signal bounce and computers are connected to the bus with the help of drop line and T-connector.

  2. Star topology: Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

  3. Ring topology: In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

  4. Mesh topology: Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

  5. Tree topology: Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

  6. Hybrid topology: if two or more topologies are combined together then it is called hybrid topology. So it is very difficult to design and to implement the hybrid topology. It is expensive too.


Network architecture

Network architecture refers to the various services provided by the network and it also deals with how data is transmitted from one computer to others.

Client server network: The client/server topology is the model for vertical scaling, where clients typically host a small subset of the data in the application process space and delegate to the server system for the rest. Compared to peer-to-peer by itself, the client/server architecture provides better data isolation, high fetch performance, and more scalability. If you expect data distribution to put a very heavy load on the network, client/server architecture usually gives better performance. In any client/server installation, the server system is itself a peer-to-peer system, with data distributed between servers. Client systems have a connection pool, which it uses to communicate with servers and other Gem Fire members. A client may also contain a local cache.

Peer-peer network: The peer-to-peer distributed system is the building block for all Gem Fire installations. Peer-to-peer alone is the simplest topology. Each cache instance, or member, directly communicates with each every other member in the distributed system. This cache configuration is primarily designed for applications that want to embed a cache within the application process space and participate in a cluster. A typical application example would be an application server cluster where the application and the cache are co-located and share the same heap.


Difference  analog and digital single

Analog signal

Digital signal

Analog signal is a continuous signal which represents physical measurements.

Digital signals are discrete time signals generated by digital modulation.

Subjected to deterioration by noise during transmission and write/read cycle.

Can be noise-immune without deterioration during transmission and write/read cycle.

More likely to get affected reducing accuracy

Less affected since noise response are analog in nature

Stored in the form of wave signal

Stored in the form of binary bit

Low cost and portable

Cost is high and not easily portable

Example: Human voice in air, analog electronic devices.

Example: Computers, CDs, DVDs, and other digital electronic devices.


Difference between Internaet and Intranet



The Internet is a worldwide, publicly accessible series of interconnected computer networks transmit data by packet switching using the standard Internet Protocol

An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organization's information or operations

This is the base, independent of the World Wide Web

Independent of the internet; however, internet is also used parallel

The Internet allows computer users to connect to other computers & information stores easily across the world; it is also used in marketing, online chat, file transfer, etc.

Intranets are being used to deliver tools & applications, helps to improve the services provided to the users, increases employees' ability to perform their jobs faster, etc.

Internet is a public computer network

Intranet is a private computer network


Signal modulation

In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal (high frequency signal), with a modulating signal that typically contains information to be transmitted.

Three forms of modulations are possible. They are as:

  1. Amplitude Modulation (AM): Amplitude modulation is an increase or decrease of the carrier voltage (Ec), will all other factors remaining constant.

  2. Frequency Modulation (FM): Frequency modulation is a change in the carrier frequency (fc) with all other factors remaining constant.

  3. Phase Modulation (PM): Phase modulation is a change in the carrier phase angle (θ). The phase angle cannot change without also affecting a change in frequency. Therefore, phase modulation is in reality a second form of frequency modulation.


Transmission media

A transmission media is defined as the means of communication between two networking devices that helps to transfer data from sender to receiver and vice versa.

Transmission media is broadly classified into two groups.

  1. Wired or Guided Media or Bound Transmission Media: Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.

  2. Wireless or Unguided Media or Unbound Transmission Media: Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. This type of transmission is called Wireless communication. Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra red are some of popular unbound transmission media.


Switching system

It provides a path between the two devices in a network. The process of transferring data blocks from one node to another node is called data switching.

Types of switching system are as follows:

  1. Circuit switching: It is the most familiar technique used to build a communication network. Used in ordinary telephone lines and it allows communications equipment and circuits to be shared among users. Each user has the sole access to a circuit during network use.

  2. Message switching: Message switching is a network switching technique in which data is routed in its entirety from the source node to the destination node, one hope at a time. During message routing, every intermediate switch in the network stores the whole message. If the entire network's resources are engaged or the network becomes blocked, the message-switched network stores and delays the message until ample resources become available for effective transmission of the message.

  3. Packet switching: A network technology that breaks up a message into small packets for transmission, unlike circuit switching, which requires the establishment of a dedicated point to point connections each packet in a packed switched network contains a destination address. Thus all packets in a single message do not have to follow the same path. Packet can arrive out of order. Destination computer reassembles the packets into their proper sequence.


OSI reference model

It is based on a proposal developed by the international organization for standardization (ISO). The model is called ISO OSI reference model, because it deals with connecting open system i.e. the system that are open for communication with other system.

1. Physical Layer: This layer concerned with transmission of bit it determines voltage level for 0 & 1. It also determines the data rate of the system. This layer involves standardized protocol dealing with electrical & signaling interface.

2. Data Link Layer: It handles error in physical layer. This layer ensures the correct delivery of frame to the destination address. It consists of 2 parts or 2 sub-layers. i.e.

  1. Logic Link Control

  2. Media Access Control

3. Network Layer: This layer is concerned with transmission of packet. N/w layer protocol chooses the best path to send a package called routing. Two protocols are widely used in n/w layer.

  1. X.25 Protocol

  2. Internet Protocol

4. Transport Layer: It provides the mechanism for the exchange of data between end systems. It ensures that the data received is in fact in order. Following jobs are performed by this layer.

  1. Port Addressing

  2. Segmentation & Reassemble

  3. Connection Control

5. Session Layer: It is responsible for requesting logical connection to be established for communication process. This logical connection is termed as session. It also provides data synchronization between two communication terminals.

6. Presentation layer: This layer translates format data to adapt to the needs of the application layer & nodes at both receiving & sending end of communication process. It handles data communication, formatting, encryption, decryption, etc.

7. Application Layer: It is the top-most layer of OSI model & provides user access to the n/w. It provides services that support user application, such as database access, email & file transfer, etc.



IP address: this is a code made up of numbers separated by three dots that identifies a particular computer on the Internet. Every computer, whether it is a Web server or the computer you're using right now, requires an IP address to connect to the Internet. IP addresses consist of four sets of numbers from 0 to 255, separated by three dots. For example "" or "". Your Internet Service Provider (ISP), will assign you either a static IP address (which is always the same) or a dynamic IP address, (which changes every time you log on).

MAC address: Stands for "Media Access Control Address," and no, it is not related Apple Macintosh computers. A MAC address is a hardware identification number that uniquely identifies each device on a network. The MAC address is manufactured into every network card, such as an Ethernet card or Wi-Fi card, and therefore cannot be changed.

Repeater: Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.

Bridge: In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).

Protocol: A standard set of regulations and requirements that allow two electronic items to connect to and exchange information with one another. Protocols regulate data transmission among devices as well as within a network of linked devices through both error control and specifying which data compression method to use. In particular, protocols decide: the method of error checking, how to compact data (if required), how the transmitting device signals that it has concluded sending data, and how the receiving device signals that it has completed receiving data.

Wi-Fi: Wi-Fi is the name of a popular wireless networking technology that uses radio waves to provide wireless high-speed Internet and network connections. A common misconception is that the term Wi-Fi is short for "wireless fidelity," however this is not the case. Wi-Fi is simply a trademarked phrase that means IEEE 802.11x.

Object Oriented Programming (OOP)

Object Oriented Programming (OOP)
Object oriented programming is a programming paradigm that was developed to overcome the drawbacks and limitations of particularly procedure oriented programming. The major need for developing such languages was to manage the ever-increasing size and complexity of programs.


Characteristics of OOP
Emphasis is on data rather than procedure.
Programs are divided into objects.
Data structures are designed such that they characterize the objects.
Functions that separate on the data of an object are tied together in the data structure.
Data is hidden and cannot be accessed by external functions.
Objects may communicate with each other through functions.
New data and functions can be easily added whenever necessary.
Bottom-up approach is followed in program design.

Advantages of OOP:
We can eliminate redundant codes by using inheritance feature of OOP.
It is very easy for managing complex and large size problems.
The most important is the reusability of codes by using the features inheritance.
It takes very less time for the development and maintaining the software.
It is efficient for testing and implementation of the system.
It follows bottom up approach.
It can be implemented in the field of OODBMS, OOAD and different fields of engineering.


OOP has several disadvantages which made it unpopular in the early years.

Size: Object oriented programs are much larger than other programs. In the early days of computing, space on hard drives, floppy drives and in memory was at a premium. Today we do not have these restrictions.
Effort: Object oriented programs require a lot of work to create. Specifically, a great deal of planning goes into an object oriented program well before a single piece of code is ever written. Initially, this early effort was felt by many to be a waste of time. In addition, because the programs were larger (see above) coders spent more time actually writing the program.
Speed: Object oriented programs are slower than other programs, partially because of their size. Other aspects of Object Oriented Programs also demand more system resources, thus slowing the program down.

Inheritance and polymorphism important feature in OOP
The process of creating a new class form an existing class in which objects of the new class inherit the attributes and behaviors of the existing class is known as inheritance. The newly created class is called derived class or child class and the class from which new class is derived is called base class or parent class. It permits the expansion and reuse of existing code without rewriting it hence, the concept of inheritance supports the concept of reusability.
The meaning of polymorphism is having many forms. It is an important feature of OOP which refers to the ability of an object to take on different forms depending upon situations. It simplifies coding and reduces the rework involved in modifying and developing an application.

Object: An object is any entity, thing or organization that exits in real world. It consists of two fundamentals characteristics: its attributes and behaviors. For example: a dog is an object having attributes such as color, weight, age, etc. and behaviors such as barking, wagging tail, etc. In OOP, attributes are represented by data and behaviors are represented by functions.

Class: A class is the collection of similar objects. It is defined as the template or prototype to define the common attributes and behavior for all the objects of the class. The entire set of data and code of an object can be made a user-defined data type with the help of a class. In fact objects are variables of type class. Once, a class has been defined,, we can create any number of objects associated with that class.

Data abstraction: In OOP, data abstraction defines the conceptual boundaries of an object. These boundaries distinguish an object from another object. So, abstraction is the act of representing essential features without including the background details. It focuses the outside view of an object, separating its essential behavior from its implementation.

Encapsulation: Encapsulation is a way if organizing data and function into a structure by concealing the way the object is implemented, that is preventing access to data by any means other than those specified. Encapsulation therefore guarantees the integrity of the data contained in the object. It implies that there is visibility to the functionalities offered by an object, and no visibility to its data.

Information Communication Technology and Cyber Law

Term Ict and it's impacts on society
ICT is applied area of computer science, electronics, telecommunication, business and of every fields that deal with processing, storing and transmitting information.


Negative impacts:
Health problem
Computer viruses
Less employment
Loss of information
Digital socialization


Digital Divide and it's Conceptualization
The digital divide refers to the gap between the have and the does not have in computers, internet access, access to information and ecommerce.


Means of connectivity or how individuals and their associates are connecting and to what like infrastructure, location, and network availability.
Intensity of connectivity, or how sophisticated are the usage like mere access, retrieval, interactivity, innovative contributions.
Purpose of connectivity or why individuals and their associates are connecting like the reasons why individuals are online and use the internet and ICT's.
Lack of connectivity which means that why individuals and their associates are not connecting.


Computer ethics and Commandments of computer  ethics
Ethics deals with placing a value on acts according to whether they are good or bad. Computer and information ethics can be understood as that branch of applied ethics which studies and analyzes such social and ethical impacts of ICT.

Do not use a computer to harm other people
Do not interfere with other people's computer work
Do not snoop or view around in other people's files
Do not use a computer to steal
Do not use or copy software for which you have not paid
Do not use other people's computer resources without authorization
Think about the social consequences of the program you write
Use a computer in ways that show consideration and respect


Intellectual property (IP)
Intellectual property (IP) refers to creations of the mind: inventions, literacy and artistic works, and symbols, names, images, and designs used in commerce. IP is divided into two categories: industrial property and copyright.

Anonymity and privacy
Anonymity means that the person does not expose his or her identity. It means outsiders cannot trace, link or observe the contents of the messages.
Privacy is the interest that the individuals have in sustaining a personal space, free from interference by other people and organizations.


Cyber law 
Cyber law is a type of law which rules in the internet to prevent internet related crime.


Fields of cyber law
Electronic and digital signature
Computer crime
Intellectual property
Data protection and privacy
Telecommunication law


Cyber law of Nepal
Nepal cannot be isolated from emerging technology and the problems raised by the technology. The cyber law is on the process of development. Nepal passed the Electronic Transaction and Digital Signature Act 2004, also known as Cyber law.
The main laws are:
The law covers most of the issues related with cyber activities and is supposed to forecast to be landmark legislation for development of IT industry in Nepal.
Conducts such as hacking, deleting data, stealing e-document, software piracy and posting offensive information are capable of criminal and civil sanctioning under the new cyber law.
The government can punish cyber offenders with up to 5 years of imprisonment and /or fine of up to Rs. 50,000. However, much depends on the harshness of the crime.
The law has tightened the security for banking transactions through electronics means, which should boost the economic activities across the internet via Nepal.
It gives legal status to information posted on the websites of government offices, government run corporations and local bodies.
It has also granted legal status to digital signatures sent through the electronic media like e-banking, e-commerce, etc.
The law has also made a new judicial body to listen to complaints, cases and matters concerning cyber crime.


Computer Crime
Computer crime has been defined broadly as a criminal act that has been committed using a computer as the primary tool.


Forms of computer crime
The theft of money, for example, the transfer of payments to the wrong accounts
The theft of information, for example, by tapping into data transmission lines or databases at no cost.
The theft of goods by their diversion to the wrong destination
The theft of computer time, for example, use of an employer's computer resources for personal work.
Besides of these, computer crime can also take form of hacking, cracking, sabotage and blackmail.


IT policies
The policies of IT are the action adopted for the implementation of strategies to achieve goals and fulfill the objectives. Some of the policies of IT are as follows:
To declare information technology sectors a prioritized sector.
To provide internet facilities to all village development committees.
To render assistance to educational institutions and encourage native and foreign training.
To computerize the records of each governmental office.
To increase the use of computers in the private sector.
To develop physical and virtual information technology park.
To use information-technology to promote e-commerce, e-education, e-health, among others.
To establish National Information Technology Centre.
To establish a national level fund by mobilizing the resources.
To establish Nepal in the global market through the use of information technology.


Term multimedia 
The term multimedia is simply a combination of multiple forms of media which includes text, graphics, audio, video, animation, etc.


The uses of multimedia
Education: we can see teachers delivering course contents using different multimedia techniques in institutions, colleges and universities which help the students for clear concept and understanding by putting designed text, audio, video, etc.
Entertainment: multimedia technology is widely used in entertainment business. Without this technology, it’s impossible to make entertainment files, movies, animation, etc.
Business: business houses give the product information to their customers through newspaper, radio, online, television whatever it may be. But gives the information attractively using multimedia tools.
Communication: in the field of communication using different sorts of multimedia tools, we can communicate with each other very easily, like live text chat, audio chat, video chat which makes our daily communication like easy.
Training: we use multimedia tools and techniques for delivering information in the form of text, image, audio, and video for trainee in attractive and effective way so that they can capture the contents easily.
Web pages: now a days, website of any organization, individuals is quite familiar for presence on NET to provide information for the users. They give the information with user friendly and interactively to the users applying different multimedia tools by using images, video, audio, animation on web page.


Components of multimedia

Graphics or images

Abbreviations and its full form
WMA: Windows Media Audio
WAV: Windows Audio Video
MIDI: Musical Instrument Digital Interface
WMV: Windows Media Video
MPEG: MOtion PIcture Experts Group/Moving Picture Expert Group/Moving
AVI: Audio Video Interleave
FLV: Flash Live Video
SWF: Small Web Format

Artificial Intelligence

Artificial Intelligence (AI) and it's application areas

Artificial Intelligence (AI) is a branch of computer science which is concerned with programs that solves and analyze problems intelligently.


The applications of AI are as:

Game playing: Ai emerges and gives new height for dull machines on the field of game playing. Some intelligence programming is far better than human brain.

Expert systems: it is computer programming to make decisions in real life situations. AI based computer system can decide and think itself for desired result what is to be happened.

Pattern detection: it detects most common patterns for authentication, for example thumb detection, iris detection, etc. This is most widely used tools for security purpose which once stored in database.

Natural Language Processing: NLP is a branch of artificial intelligence that deals with analyzing understanding and generating the languages that human use naturally in order to interface with computers in both written and spoken.

Automated operation: AI is used to automate satellite, space shuttle, airplane without pilot, etc. Without any technical human being, the system automatically handle a and controls the systems that are already set in that corresponding instruction with logics and mathematics.

Robotics: robots are used in many fields like in space, medicine, and research etc. Now a days, robots are broadly using in surgery for operation micro level surgery for operation micro-level surgery.


components of AI

Search: this intelligence is used to search solution of particular problem like possibilities of moves on chess playing game. Searching is very important and needs to be very fast and must search with accuracy. So AI based system is useful for particular problem oriented search easily.

Pattern recognization: it is used to recognize some type of figures, images or audio sounds. Its application is used for the authentication like face detection, iris detection, voice recognization, etc.

Logic generate: as the name suggest, AI is intelligence with creating logic in different problems. Logic in terms of predicate basis or whatever, this system creates logic for solving the any kind of related problems as per the AI related system and software.

Common sense and reasoning: the main goal of AI is to produce good reasoning power and produce logic. This reasoning power and logic made machines like human.

Learning from experience: AI programming is built to learn from the experiences like human being. Although learning are limited with comparison to the human beings and also depends on the programming language used.

Genetic programming: AI programs are used to solve relationship between humans. As we see in genetically there is inheritance properties that can help the future prediction.

Neural network: AI technique that mimics the operation of the human brain that refers to nerves and neurons, and comprises of densely interconnected processors working simultaneously that means parallel.


Ethical aspect of AI

AI can be used for good or bad. This is why it's important to think about what AI is, and how we want it to be used.

Some ethical aspects of AI are:

AI builders have an obligation not to exploit people's ignorance and make them think. AI is human.

Robots are not really your friends. They may be harmful for individuals. So developers should be ethical. Use of AI must obey the social norms and values.

Use of AI should be under the intellectual property rights.

Contemporary Technology

e-Commerce and e-business

E-commerce refers to online transactions, buying and selling of goods and/or services over the internet.

E-business covers online transactions, but also extends to all internets based interactions with business partners, suppliers and customers.


Advantages of e-commerce:

a.  It makes buying selling procedure faster, as well as easy to find products.

b.  It makes buying/selling possible 24/7.

c.  There are no theoretical geographical limitations hence more reach to customers.

d.  It reduces operational costs and provides better quality of services.

e. It does not require physical company set ups.

f.  It is easy to start and manage a business.


Disadvantages of e-commerce:

a. Any one, good or bad can easily start a business. And there are many bad sites which eat up customer's money.

b. There is no guarantee of product quality.

c.  Mechanical failures can cause unpredictable effects on the total processes.

d. As there is minimum chance of direct customer to company interactions, customer loyalty is always on a check.

e. There are many hackers who look for opportunities and thus an ecommerce site, service payment gateways all are always prone attack.



E-learning is a new concept of delivering digital contents in learner oriented environment using information and communication te4chnology (ICT). Delivery of the digital content is the main characteristic of e-learning.


Advantages of e-learning:

It maintains the consistency of content.

It is easy for customization.

There is no any geographical limitation for learning.

It is quite favorable for learner as it can happen at any time and anywhere.

It reduces or eliminates travel costs to attend learning events.

It reduces or eliminates need for classroom/instructor infrastructure.


Disadvantages of e-learning:

Learners with low motivation or bad study habits may fall behind

Without the routine structures of a traditional class, students may get lost or confused about course activities and deadlines

Students may feel isolated from the instructor and classmates

Instructor may not always be available when students are studying or need help

Slow Internet connections or older computers may make accessing course materials frustrating

Managing computer files and online learning software can sometimes seem complex for students with beginner-level computer skills

Hands-on or lab work is difficult to simulate in a virtual classroom.



E-governance is the application of electronic means to improve the interaction between government and citizens; and to increase the administrative effectiveness and efficiency in the internal government operations.

Despite the government of Nepal has positively giving attention towards the development of ICTs and subsequent implementing e-governance, a number of issues has yet addressed. Some of the challenges for successful implementation of e-governance are presented as:

Information transparency

Legal issues

Resources availability

Infrastructure including connectivity in rural area

Capacity and awareness

Political will and government action


Advantages of E-governance

E-Governance offers many benefits and advantages for the government, corporate sector and society. E-Governance facilitates better delivery of government services to citizens, improved interactions with business and industry, citizen empowerment through access to information, or more efficient government management. It simplifies internal operations and improves performance of government departments while helping all sections of society to avail government services at lower cost with maximum ease of use.



Virtual reality

Virtual reality is a new computational paradigm that redefines the interface between human and computer becomes a significant and universal technology and subsequently penetrates applications for education and learning.


Application fields of Virtual reality

Virtual Reality in the Military: A virtual reality simulation enables them to do so but without the risk of death or a serious injury. They can re-enact a particular scenario, for example engagement with an enemy in an environment in which they experience this but without the real world risks.

Virtual Reality in Education: Education is another area which has adopted virtual reality for teaching and learning situations. The advantage of this is that it enables large groups of students to interact with each other as well as within a three dimensional environment.

Virtual Reality in Healthcare: Healthcare is one of the biggest adopters of virtual reality which encompasses surgery simulation, phobia treatment, robotic surgery and skills training.

Virtual Reality in Business: Many businesses have embraced virtual reality as a cost effective way of developing a product or service. For example it enables them to test a prototype without having to develop several versions of this which can be time consuming and expensive.

Virtual Reality in Engineering: Virtual reality engineering includes the use of 3D modelling tools and visualization techniques as part of the design process. This technology enables engineers to view their project in 3D and gain a greater understanding of how it works. Plus they can spot any flaws or potential risks before implementation.

Virtual Reality and Scientific Visualization: Virtual reality is being increasingly used in the field of scientific visualization. This field is based upon using computer graphics to express complex ideas and scientific concepts, for example molecular models or statistical results.

Virtual Reality Programming Languages: For virtual reality to be truly effective, it must have a good sense of realism. Just on its own this is a technical challenge and, as such, virtual reality is highly demanding on many resources. From hardware performance to the intellectual ability of the implementer of the system, how these are managed are a massive issue.




E-medicine refers to an approach that provides medical services whenever and wherever required using information and communication technology.

With the help of this approach, even small number of doctors can provide medical service to large number of people scattered in different locations. The people of rural areas who are unable to get service of doctors can be benefitted from this approach. The patients share his/her medical problems to the doctors. This approach is now getting more popularity among the doctors too. They can post their experiences and issues in the online discussion forum. Without good facility of information and communication technology, e-medicine cannot be effective. This is the problem facing in the developing countries like Nepal.



Impact of Robotics in human life

Positive Impacts:

Robots can provide a wide variety of benefits to society. The most prominent benefit of robots is that they allow physical tasks to be performed at a greater speed than humans could reasonably achieve, and that tasks can be performed by robots that are beyond the reasonable physical capabilities of humans. For example, in manufacturing, mechanized processes allow production to take place at a great speed, with little human effort required. This allows for the low-cost mass-production of goods. These manufacturing processes allow for great precision, and can allow products of a very high quality to be produced.

Negative Impacts:

As they are out to use to do common tasks, Humans are increasingly becoming lazy, and thus their health is adversely affected. Also, as robots become more and more autonomous, the chances that they commit a mistake are very high. These mistakes can lead to serious problems if unchecked. Also, as self-learning Robots evolve, they may make decisions that are harmful to Human beings. From another perspective, If the robots are not self-learning, they will do jobs only which they are programmed for. Updating their functions will thus require more expertise.