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Operating System

Introduction of Operating System

An operating system acts as an intermediary between the user of a computer and computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient and efficient manner.

An operating system is a software that manages the computer hardware. The hardware must provide appropriate mechanisms to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.

Operating System – Definition:

An operating system is a program that controls the execution of application programs and acts as an interface between the user of a computer and the computer hardware.
A more common definition is that the operating system is the one program running at all times on the computer (usually called the kernel), with all else being application programs.
An operating system is concerned with the allocation of resources and services, such as memory, processors, devices, and information. The operating system correspondingly includes programs to manage these resources, such as a traffic controller, a scheduler, memory management module, I/O programs, and a file system.

Functions of Operating system – Operating system performs three functions:

Convenience: An OS makes a computer more convenient to use.
Efficiency: An OS allows the computer system resources to be used in an efficient manner.
Ability to Evolve: An OS should be constructed in such a way as to permit the effective development, testing and introduction of new system functions at the same time without interfering with service.

Operating system as User Interface –

User
System and application programs
Operating system
Hardware

Every general-purpose computer consists of the hardware, operating system, system programs, and application programs. The hardware consists of memory, CPU, ALU, and I/O devices, peripheral device, and storage device. System program consists of compilers, loaders, editors, OS, etc. The application program consists of business programs, database programs.

Conceptual View of a Computer System

Every computer must have an operating system to run other programs. The operating system coordinates the use of the hardware among the various system programs and application programs for various users. It simply provides an environment within which other programs can do useful work.

The operating system is a set of special programs that run on a computer system that allows it to work properly. It performs basic tasks such as recognizing input from the keyboard, keeping track of files and directories on the disk, sending output to the display screen and controlling peripheral devices.
OS is designed to serve two basic purposes:

It controls the allocation and use of the computing System’s resources among the various user and tasks.
It provides an interface between the computer hardware and the programmer that simplifies and makes feasible for coding, creation, debugging of application programs.

The Operating system must support the following tasks. The task are:

Provides the facilities to create, modification of programs and data files using an editor.
Access to the compiler for translating the user program from high level language to machine language.
Provide a loader program to move the compiled program code to the computer’s memory for execution.
Provide routines that handle the details of I/O programming.

I/O System Management –
The module that keeps track of the status of devices is called the I/O traffic controller. Each I/O device has a device handler that resides in a separate process associated with that device.
The I/O subsystem consists of

A memory Management component that includes buffering caching and spooling.
A general device driver interface.

Drivers for specific hardware devices.

Assembler –
The input to an assembler is an assembly language program. The output is an object program plus information that enables the loader to prepare the object program for execution. At one time, the computer programmer had at his disposal a basic machine that interpreted, through hardware, certain fundamental instructions. He would program this computer by writing a series of ones and Zeros (Machine language), place them into the memory of the machine.

Compiler –
The High-level languages- examples are FORTRAN, COBOL, ALGOL and PL/I are processed by compilers and interpreters. A compiler is a program that accepts a source program in a “high-level language “and produces a corresponding object program. An interpreter is a program that appears to execute a source program as if it was machine language. The same name (FORTRAN, COBOL, etc.) is often used to designate both a compiler and its associated language.

Loader –
A Loader is a routine that loads an object program and prepares it for execution. There are various loading schemes: absolute, relocating and direct-linking. In general, the loader must load, relocate and link the object program. The loader is a program that places programs into memory and prepares them for execution. In a simple loading scheme, the assembler outputs the machine language translation of a program on a secondary device and a loader places it in the core. The loader places into memory the machine language version of the user’s program and transfers control to it. Since the loader program is much smaller than the assembler, those make more core available to the user’s program.

History of Operating system –
Operating system has been evolving through the years. Following Table shows the history of OS.

GENERATION	YEAR	ELECTRONIC DEVICE USED	TYPES OF OS DEVICE
First	1945-55	Vaccum Tubes	Plug Boards
Second	1955-65	Transistors	Batch Systems
Third	1965-80	Integrated Circuits(IC)	Multiprogramming
Fourth	Since 1980	Large Scale Integration	PC

Types of Operating System –

Batch Operating System- Sequence of jobs in a program on a computer without manual interventions.
Time sharing operating System- allows many users to share the computer resources.(Max utilization of the resources).
Distributed operating System- Manages a group of different computers and make appear to be a single computer.
Network operating system- computers running in different operating system can participate in common network (It is used for security purpose).
Real time operating system – meant applications to fix the deadlines.

Examples of Operating System are –

Windows (GUI based, PC)
GNU/Linux (Personal, Workstations, ISP, File and print server, Three-tier client/Server)
macOS (Macintosh), used for Apple’s personal computers and work stations (MacBook, iMac).
Android (Google’s Operating System for smartphones/tablets/smartwatches)
iOS (Apple’s OS for iPhone, iPad and iPod Touch)

References –
Operating System Concepts – Book
Introduction to Operating System – NPTEL

Goals of Networks & advantages and disadvantages of networking

Fahad V S IT ,

Networks

Computer Network means an interconnection of autonomous (standalone) computers for information exchange. The connecting media could be a copper wire, optical fiber, microwave or satellite.

Networking Elements – The computer network includes the following networking elements:

At least two computers
Transmission medium either wired or wireless
Protocols or rules that govern the communication
Network software such as Network Operating System

Network Criteria:

The criteria that have to be met by a computer network are:

1. Performance – It is measured in terms of transit time and response time.

Transit time is the time for a message to travel from one device to another
Response time is the elapsed time between an inquiry and a response.

Performance is dependent on the following factors:

The number of users
Type of transmission medium
Capability of connected network
Efficiency of software

2. Reliability – It is measured in terms of

Frequency of failure
Recovery from failures
Robustness during catastrophe

3. Security – It means protecting data from unauthorized access.

Goals of Computer Networks: The following are some important goals of computer networks:

Resource Sharing –

Many organization has a substantial number of computers in operations, which are located apart. Ex. A group of office workers can share a common printer, fax, modem, scanner etc.
High Reliability –

If there are alternate sources of supply, all files could be replicated on two or, machines. If one of them is not available, due to hardware failure, the other copies could be used.
Inter-process Communication –

Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications.
Flexible access –

Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another.

Other goals include Distribution of processing functions, Centralized management, and allocation of network resources, Compatibility of dissimilar equipment and software, Good network performance, Scalability, Saving money, Access to remote information, Person to person communication etc.,

Advantages and Disadvantages of Computer Networking

Computer network is defined as a set of interconnected autonomous systems that facilitate distributed processing of information. It results in better performance with high speed of processing.

Advantages of Network:

These are main advantages of Computer Networks:

Central Storage of Data –

Files can be stored on a central node (the file server) that can be shared and made available to each and every user in an organization.
Anyone can connect to a computer network –

There is a negligible range of abilities required to connect to a modern computer network. The effortlessness of joining makes it workable for even youthful kids to start exploiting the data.
Faster Problem solving –

Since an extensive procedure is disintegrated into a few littler procedures and each is taken care of by all the associated gadgets, an explicit issue can be settled in lesser time.
Reliability –

Reliability implies backing up of information. Due to some reason equipment crash, and so on, the information gets undermined or inaccessible on one PC, another duplicate of similar information is accessible on another workstation for future use, which prompts smooth working and further handling without interruption.
It is highly flexible –

This innovation is known to be truly adaptable, as it offers clients the chance to investigate everything about fundamental things, for example, programming without influencing their usefulness.
Security through Authorization –

Security and protection of information is additionally settled through system. As just the system clients are approved to get to specific records or applications, no other individual can crack the protection or security of information.
It boosts storage capacity –

Since you will share data, records and assets to other individuals, you need to guarantee all information and substance are legitimately put away in the framework. With this systems administration innovation, you can do the majority of this with no issue, while having all the space you requirement for capacity.

Disadvantages of Network:

These are main disadvantages of Computer Networks:

It lacks robustness –

If a PC system’s principle server separates, the whole framework would end up futile. Also, if it has a bridging device or a central linking server that fails, the entire network would also come to a standstill. To manage these issues, gigantic systems ought to have a ground-breaking PC to fill in as document server to influence setting to up and keeping up the system less demanding.
It lacks independence –

PC organizing includes a procedure that is worked utilizing PCs, so individuals will depend a greater amount of PC work, rather than applying an exertion for their jobs that needs to be done. Beside this, they will be subject to the primary document server, which implies that, in the event that it separates, the framework would end up futile, making clients inactive.
Virus and Malware –

On the off chance that even one PC on a system gets contaminated with an infection, there is a possibility for alternate frameworks to get tainted as well. Infections can spread on a system effectively, in view of the between availability of different gadgets.4. Lack of Independence
Cost of network –

The expense of executing the system including cabling and equipment can be expensive.

PC systems administration will dependably be a quick and advantageous methods for exchanging and sharing data, yet individuals ought to know about its outcomes too.

Networking Concepts! Are they Real?

Fahad V S IT ,

Let’s experiment with Networking

Most of us have studied Computer Networks in a very abstract manner. In other words, not many of us know how the abstract concepts of layers and packets translate in real life networks such as the Internet. Therefore let us do an experiment and see whether these layers, packets etc. exist in any real network also. So get, set and ready to delve into this wonderful world of practical and experimental Networking!

The outline of our experiment is as follows. We will capture some live packets, and to understand what is inside those packets, we will analyze those packets by dissecting them.

To start with, we need to have a PC running Windows XP and connected to the Internet. If you are reading this article online, the chances are high that you have everything ready to experiment. Now let’s recall some of the theory stuff that we read in Networking Books. The first thing that almost every book tells us – networking architecture is layered; remember that 7 layer OSI protocol stack! So where are these protocol layers? In our experiment, we will use 5 layer Internet Protocol stack so that we can solve the mystery of these layers.

We start our experiment by installing Wireshark (earlier known as Ethereal). Wireshark is a Network Protocol Analyzer that can capture and analyze the packets transmitted/received via a Network Interface Card (NIC). [You need to bear with me this acronym because Networking is full of acronymsJ] We install Wireshark from http://www.wireshark.org/download.html (at the time of this writing, the latest Wireshark version is 1.0.3). While installing Wireshark, leave the default settings/options as it is. Now our experimental setup is ready. Run Wireshark and click on the first icon (List the available capture interfaces …). Now we see a pop up window that shows Capture Interfaces. See the snapshots as follows.

The number and types of interfaces shown in Capture Interfaces window can be different for you depending on your PC’s configuration. For me it shows two interfaces and my Internet connection is through Broadcom Gigabit Interface. So choose the interface through which your Internet connection is available to you. Now let’s click on the Options button of this interface. Now we see a new window named Capture Options. In this window, type “port 80” in text field named Capture Filter. See the following snapshot for clarification.

Now we are ready to capture the packets passing through our NIC. By setting the filter to “port 80”, we have instructed Wireshark to capture only those packets that are because of http traffic (remember that we were always told that the default http port is 80!). Now click on the Start button on Capture Options window. You may see some packets in Wireshark if any program in your PC is accessing http traffic in the background; let’s not focus on that. Now open your browser and try to access http://google.com and now you should be seeing lot many packets getting captured in Wireshark. See the snapshot as follows.

Let’s start analyzing the captured packets. First of all, find the first instance of http packet that has GET / HTTP/1.1 in its Info field. In the above snapshot, it’s shown in blue. If we take a closer look, we see that this packet has the headers of the all the 5 layers of the Internet Protocol stack.

Layer 1 – It is the Physical layer. Here Frames are shown at the physical layer.

Layer 2 – It is the Data Link layer. In this packet, we can see that Ethernet II is used as data link layer protocol. We can find the MAC address of the source and destination in this header.

Layer 3 – It is the Network layer. In this packet, we see that IP is used as Network layer protocol. We can see the source and destination IP in this header.

Layer 4 – It is the Transport layer. In this packet, TCP is used as Transport layer protocol. We can find the source and destination ports in this header.

Layer 5 – It is the Application layer. In this packet, HTTP is used as Application layer protocol.

Let’s explore one of the layers. Other layers can be explored further in the similar fashion. If we expand the Layer 5 i.e. HTTP header, it looks as follows.

Here we see that Host is mentioned as google.com that is what we tried to access from browser. User Agent field of the HTTP header shows the browser details. In my case, it is Mozilla Firefox as evidenced from this header. Destination IP 64.233.187.99 should be one of the IP addresses assigned to Google server where the web server is hosted. It can be verified using a very handy utility command “nslookup”. The details of the other fields can be explored in the headers of the HTTP, TCP, IP, Ethernet II protocols. Some of the interesting fields are – Differentiated Services Field (also known as QoS field) in IP header, Window size in TCP header etc.

So we have seen that all those rhetorical concepts of layers etc. do exist in real networks also. And it sounds interesting when you dissect all the packets that pass through your interface card. By doing so, you can get to know what goes/comes through your PC!

The idea of this experiment is to provide a conducive platform so that you can explore your own the exciting world of Networking. So welcome aboard!

The Internet and the Web

Fahad V S IT ,

1. The Internet:

In simplest words it is a global network of smaller networks interconnected using communication protocols that are standardised. The Internet standards describe a framework known as the Internet protocol suite. This model divides methods into a layered system of protocols.

These layers are as follows:

Application layer (highest) – concerned with the data(URL, type, etc), where HTTP, HTTPS, etc comes in.
Transport layer – responsible for end-to-end communication over a network.
Network layer – provides data route.

Provides a variety of information and communication facilities; contains forums, databases, email, hypertext, etc. It consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies.

2. The World Wide Web:

The web is a subset of the internet. It’s a system of Internet servers that support specially formatted documents. The documents are formatted in a markup language called HTML (that supports links, multimedia, etc). These documents are interlinked using hypertext links and are accessible via the Internet.

To link hypertext to the Internet, we need:

The markup language, i.e., HTML.
The transfer protocol, e.g., HTTP.
Uniform Resource Locator (URL), the address of the resource.

We access the web using web browsers.

Difference between Web and Internet:

INTERNET	WEB
Internet is the library and web a collection of books. The internet also consists of databases, email, forums, etc.	Web is a subset of the internet. The web is a large portion of the internet but it isn’t all of it.
The internet is a network, a way of transporting content and web lets us use that content.	The Web is ideally a way of accessing information over the medium of the Internet. Web is a collection of internet servers that can host HTML formatted documents. A collection of pages, of information connected to each other around the globe. Each page can be a combination of text and multimedia.

URI:

URI stands for ‘Uniform Resource Identifier’, it’s like an address providing a unique global identifier to a resource on the Web. Uniform Resource Locator (URL) is the most commonly used form of a URI.

The URL consists mainly of two parts:

The protocol used in transfer, e.g., HTTP.
The domain name.

Who governs the Internet?

The Internet is not governed, it has no single authority figure. The ultimate authority for where the Internet is going rests with the Internet Society, or ISOC.

ISOC is a voluntary membership organization whose purpose is to promote global information exchange through Internet technology.

ISOC appoints the IAB- Internet Architecture Board. They meet regularly to review standards and allocate resources, like addresses.
IETF- Internet Engineering Task Force. Another volunteer organisation that meets regularly to discuss operational and technical problems.

Robots

Shilpa IT ,

Robots Among Us

It is not the mechanical “body” that is unattainable; articulated arms and other moving mechanisms adequate for manual work already exist, as the industrial robots attest. Rather it is the computer-based articial brain that is still well below the level of sophistication needed to build a humanlike robot.

The challenge facing roboticists is to take general-purpose computers and program them to match the largely special-purpose human brain, with its ultraoptimized perceptual inheritance and other peculiar evolutionary traits. Today’s robot-controlling computers are much too feeble to be applied successfully in that role, but it is only a matter of time before they are up to the task.

Molecular biology and neuroscience are steadily uncovering the physical mechanisms underlying life and mind but so far have addressed mainly the simpler mechanisms. Evidence that simple functions can be composed to produce the higher capabilities of nervous systems comes from programs that read, recognize speech, guide robot arms to assemble tight components by feel, classify chemicals by articial smell and taste, reason about abstract matters, and so on. Of course, computers and robots today fall far short of broad human or even animal competence. But that situation is understandable in light of an analysis, summarized in the next section, that concludes that today’s computers are only powerful enough to function like insect nervous systems. And, in my experience, robots do indeed perform like insects on simple tasks.

Though dispiriting to articial-intelligence experts, the huge decit does not mean that the goal of a humanlike articial brain is unreachable.

Commercial mobile robots have found few jobs. The largest class of commercial mobile robots, known as automatic guided vehicles (AGVs), transport materials in factories and warehouses. Most follow buried signal-emitting wires and detect end points and collisions with switch.

It costs hundreds of thousands of dollars to install guide wires under concrete oors, and the routes are then xed, making the robots economical only for large, exceptionally stable factories.

The most advanced industrial mobile robots,for instance, laser-sensed bar codes—and by preexisting features such as walls, corners and doorways. The costly labor of laying guide wires is replaced by custom software that is carefully tuned for each route segment. The small companies that developed the robots discovered many industrial customers eager to automate transport, oor cleaning, security patrol and other routine jobs. Alas, mos buyers lost interest as they realized that installation and route changing required time-consuming and expensive work by experienced route programmers of inconsistent availability.

Physical properties include shape, weight, strength, texture and appearance of things, and ways to handle them. Psychological factors, applied to humans and robots alike, include goals, beliefs, feelings and preferences. Developing the simulators will be a huge undertaking involving thousands of programmers and experience-gathering robots.

Basics of Computer Networking.

Fahad V S IT ,

Computer Network is the interconnection of multiple devices, generally termed as Hosts connected using multiple paths for the purpose of sending/receiving data or media.There are also multiple devices or mediums which helps in the communication between two different devices which are known as Network devices. Ex: Router, Switch, Hub, Bridge.The layout pattern using which devices are interconnected is called as network topology. Such as Bus, Star, Mesh, Ring, Daisy chain

Open system: A system which is connected to the network and is ready for communication.

Closed system: A system which is not connected to the network and can’t be communicated with.

OSI
Protocol

UNIQUE IDENTIFIERS OF NETWORK

Host name
IP Address (Internet Protocol address)
MAC Address (Media Access Control address)
Port
Socket

OSI stands for Open Systems Interconnection. It is a reference model that specifies standards for communications protocols and also the functionalities of each layer.A protocol is the set of rules or algorithms which define the way how two entities can communicate across the network and there exists different protocol defined at each layer of the OSI model. Few of such protocols are TCP, IP, UDP, ARP, DHCP, FTP and so on.

Each device in the network is associated with a unique device name known as Hostname.Type “hostname” in the command prompt(Administrator Mode) and press ‘Enter’, this displays the hostname of your machine.

Also, known as the Logical Address, is the network address of the system across the network.To identify each device in the world-wide-web, Internet Assigned Numbers Authority (IANA) assigns IPV4 (Version 4) address as a unique identifier for each device on the Internet.Length of the IP address is 32-bits. (Hence we have 232 IP addresses available.)Type “ipconfig” in the command prompt and press ‘Enter’, this gives us the IP address of the device.

Also known as physical address, is the unique identifier of each host and is associated with the NIC (Network Interface Card).MAC address is assigned to the NIC at the time of manufacturing.Length of the MAC address is : 12-nibble/ 6 bytes/ 48 bits.Type “ipconfig/all” in the command prompt and press ‘Enter’, this gives us the MAC address.

Port can be referred as a logical channel through which data can be sent/received to an application. Any host may have multiple applications running, and each of this application is identified using the port number on which they are running.Port number is a 16-bit integer, hence we have 2^16 ports available.

The unique combination of IP address and Port number together are termed as Socket.

Operating System

Introduction of Operating System

Goals of Networks & advantages and disadvantages of networking

Networks

Computer Network means an interconnection of autonomous (standalone) computers for information exchange. The connecting media could be a copper wire, optical fiber, microwave or satellite.

Network Criteria:

Advantages and Disadvantages of Computer Networking

Networking Concepts! Are they Real?

Let’s experiment with Networking

The Internet and the Web

Robots

Robots Among Us

Though dispiriting to articial-intelligence experts, the huge decit does not mean that the goal of a humanlike articial brain is unreachable.

Commercial mobile robots have found few jobs. The largest class of commercial mobile robots, known as automatic guided vehicles (AGVs), transport materials in factories and warehouses. Most follow buried signal-emitting wires and detect end points and collisions with switch.

It costs hundreds of thousands of dollars to install guide wires under concrete oors, and the routes are then xed, making the robots economical only for large, exceptionally stable factories.

Basics of Computer Networking.

UNIQUE IDENTIFIERS OF NETWORK

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