Types of Operating System

Type of Operating System



• Batch Operating System

It do not interact with computer directly. Each user prepare his job on an offline device like punch card and submit it to the computer operator. To speed up processing jobs, with similar job batched together and run as a group. The programmer leave their programs with the operator and the operator then so store the program with similar requirement into batches.

Disadvantage

1. lack of interaction between the user and the job.
2. CPU is often Idle, because the speed of the mechanical input device is slower then the CPU.
3. Difficult to provide the desired priority.

 

• Time Sharing Operating System

Time sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time sharing or multitasking is a logical extension of multiprogramming .Processor's time which is shared among multiple users simultaneously is termed as time sharing.

Multiple jobs are executed by the CPU by switching between them but the switching occur so frequently. Thus the user get immediate response.

For example:- In a transaction processing , the processor executes each user program in a short burst or quantum of computation. That is , if n user are present then each user can get a time quantum .

Advantage

1. provide the advantage of quick response.
2. Avoid duplication of software.
3. Reduces CPU idle time.

Disadvantage

1. Problem of reliability.
2. Question of security and integrity.
3. Problem of data communication. 

• Distributed Operating System

Distributed application are running on Multiple computers linked by communication. A distribution operating system is an extension of the network operation that supports higher levels of communication and integration of the machines on the network. processor in a distributed system may vary in size and function. These processors are referred as sites , node, computers.

• Network Operating System

Network Operating system run on server and provides the server the capability to manage data, user, group, security, application and other network function. It allow shared file and printer access among multiple computers in network(LAN), private network or other network.

For example:- MS window server 2003, Microsoft window server 2008, UNIX, Linux, MACOSX.

Advantage

1. Centralized servers are highly stable.
2. Security is server managed. 
3. Upgrade to new technologies and hardware can be easily integrated into the system.
4. Remote access to server is possible from different location and type of system.

Disadvantage

1. High cost of buying and running a server.
2. Dependency on a central location for most operation
3. Regular maintenance and update required.

 

What is Operating System

• ·   It acts as an intermediary between a user of a computer and the computer hardware. Operating system is to provide an environment in which a user can execute programs in a convenient and efficient manner. All computer programs, excluding firmware, require an operating system to function.

• ·        Time sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.

• ·        For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer –from cellular phones and video game consoles to web servers and supercomputers.

 

what is Object Oriented Programming

OOP is a technique to develop logical modules, such as classes that contains properties, fields and events. Object-Oriented Programming is a methodology or paradigm to design a program using classes and objects. It simplifies the software development and maintenance by providing some concepts:

• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

Simula is considered as the first object-oriented programming language.

What is Class

Class is basic building block of OOP. A class contains data and behavior of entity.

What is an Object?

Object is an instance of a class. Any entity that has state and behavior is known as an object.

For example: chair, pen, table, keyboard, bike etc. It can be physical and logical. An object has three characteristics:

• State:- represents data (value)of an object.
• behavior(functionality):-represents the functionality of an object.
• identity:-object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user. But it is used internally by the compiler to identify each object uniquely.

For example "keyboard" is an object .Its name dell color black know as its state. It is used for typing so, typing is it behavior.

Class is a template or blueprint from which object are created.  So object is the instance of a class.

Difference between Procedure/structure oriented programming and object oriented programming

Procedure/ structure oriented Programming

• Conventional programming, using high level languages such as COBOL, FORTRAN and C, is

commonly known as procedure-oriented programming (POP).

• In the procedure-oriented approach, the problem is viewed as a sequence of things to be done

such as reading, calculating and printing. A number of functions are written to accomplish these

tasks.

• The primary focus is on functions.

Object Oriented Programming

• Emphasis is on data rather than procedure.

• Programs are divided into what are known as objects.

• 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.

What is Java

Java is a programing language purpose computer programming language that is concurrent, class-based, object-oriented and specifically designed to have as few implementation dependencies as possible. Java can be write once and run anywhere(WORA). Meaning that compiled Java code can run on all platforms that support Java without the need for recompilation

Software development life cycle(SDLC)

1. Requirement gathering and analysis
2. Design
3. Implementation or coding
4. Testing
5. Deployment
6. Maintenance

Phase 1: Requirement gathering and analysis

This phase emphasizes on four question

1. what?
2. why?
3. Collecting data and details?
4. how? 

These are general questions that get answered during a requirements gathering phase. After requirement gathering these requirements are analyzed for their validity and the possibility of incorporating the requirements in the system to be development is also studied. Finally, a Requirement Specification document is created which serves the purpose of guideline for the next phase of the model.

Phase 2: Defining Requirements

Once the requirement analysis is done the next step is to clearly define and document the product requirements and get them approved from the customer or the market analysts. This is done through an SRS (Software Requirement Specification) document which consists of all the product requirements to be designed and developed during the project life cycle.



Phase 3: Designing

Designing is a heart of SDLC. Once the planning is done the designing (programing) of the desired solution begins.

 Phase 4:Testing

Once the solution(software) is programmed it needs to be tested on different grounds with variable intensities. This stage is usually a subset of all the stages as in the modern SDLC models, the testing activities are mostly involved in all the stages of SDLC. However, this stage refers to the testing only stage of the product where product defects are reported, tracked, fixed and retested, until the product reaches the quality standards defined in the SRS.

Phase 5: Implementation

Final implementation is done after the proper testing and approval from the client.





Phase 6: Maintenance

After the deployment of solution the maintenance is a key point that should never be omitted. Once when the customers starts using the developed system then the actual problems comes up and needs to be solved from time to time. This process where the care is taken for the developed product is known as maintenance.

• Monthly Maintenance
• Quarterly Maintenance
• Annual Maintenance





SDLC Models

SDLC models are a package of steps and procedure, which may differ model wise. Following are the most important and popular SDLC models followed in the industry:

•  Waterfall Model

• Iterative Model

• Spiral Model

• V-Model

• Big Bang Model

Other related methodologies are Agile Model, RAD Model, Rapid Application Development and Prototyping Models.

Waterfall Model

Waterfall model is a basic approach of SDLC implementation. It is also know as linear sequential life cycle model. It is very easy to use and understand. In waterfall model each phase must be complete before next to be start. Top to down approach is followed. The flow of data and control is accomplished process by process.



Design:

Advantage:

• It is easy to manage due to the rigidity of the model – each phase has specific deliverables and a review process.
• Waterfall model works well for smaller projects where requirements are very well understood.
• This model is simple and easy to understand and use.
• In this model phases are processed and completed one at a time. Phases do not overlap.

Disadvantage:

• Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage.
• No working software is produced until late during the life cycle.
• High amounts of risk and uncertainty.
• Not a good model for complex and object-oriented projects.
• Poor model for long and ongoing projects.
• Not suitable for the projects where requirements are at a moderate to high risk of changing

Network Architecture

Network Architecture is the complete framework of an organization's computer network. It include component used for communication, cabling and device types , network layout and typologies , physical and future plans. This architecture is always designed by a network manager/administrator with coordination of network engineers and the other design engineers.

1. Peer to Peer
2. Client server

Peer to peer is a commonly used computer network in which each workstation, node  has the same capabilities and responsibilities. Peer to peer may also used to refer to a single software program design so that each instance of the program may act as both client and server with the same responsibilities and status.

Client Server is a network architecture in which each computer or process on the network is either a client or a server. Server are powerful computer or processors dedicated to managing disk drive, printer or network traffic(network server). Client are PC or workstation on which user run application.

Code Structure in Java

Source file

Source file holds one class definition. The class represents a piece of your program, although a very tiny application might need just a single class. Source file code with .java extension .

Class 

A Java class file is a file (with the .class filename extension) containing Java byte code that can be executed on the Java Virtual Machine (JVM). A Java class file is produced by a Java compiler from Java programming language source files(.java files) containing Java classes.The class must go with a pair of curly braces({}). A class has one or more methods.

Method

A method is a set of code which is referred to by name and can be called (invoked) at any point in a program simply by utilizing the method's name. Think of a method as a subprogram that acts on data and often returns a value. Each method has its own name. Method code is basically a set of statement and for now you can think a method kind of like a function or procedure.

ISO-OSI Model

• ISO-OSI (International Standard Organization - Open System Interconnection)
• The ISO-OSI model is a seven layer architecture. It defines seven layers or levels in a complete communication system.
• OSI model defines a network framework to implement protocols in server layer.
• Control is passed from one layer to the next, starting at the application layer in one station and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Application

↓

Presentation layer

↓

Session layer

↓

Transport Layer

↓

Network layer

↓

Data link layer

↓

Physical layer

Layer 1-Physical layer

The Physical layer of the OSI model is responsible for transmission of digital data bits from the Physical layer of the sending (source) device over network communications media to the Physical layer of the receiving (destination) device. It deal with communication media receives frame from data link layer and converted them in bits. It converts the digital/analog bits into electrical signal or optical signals. Data encoding is done.

Layer 2- Data link layer

Data link obtain data from physical layer and check for errors. Main function is defining the media access control or hardware address. Define how the network layer protocol is encapsulated in the data link layer frame. It provided both connection-less and connection-oriented services.

Layer 3-Network layer

Network layer provide logical address know as IP address .Router works on this layer. Main function define IP address.Find routes based on IP address to reach its destination. connect different data link type together like as token ring , serial, IDDI , Ethernet etc.