May 2020

Introduction to Operating Systems

A Computer consists of hardware, firmware and software. Any physical component of a computer system with a definite shape is called a hardware. Examples of hardware include: mouse, keyboard, display unit, hard disk, speaker, printer etc. The booting instructions stored in the ROM (Read Only Memory) are called firmware. The initial text information displayed on the screen are displayed by firmware.

How the initial operations of a computer are performed

  • When the user powers up the computer the CPU (Central Processing Unit) activates the BIOS (Basic Input Output System).
  • The first program activated is POST (Power On Self-Test). Using the CMOS (Complementary Metal Oxide Semiconductor) memory this checks all the hardware and confirms that all are functioning properly.
  • After that it reads the MBR (Master Boot Record) in boot drive in accordance with the firmware ‘bootstrap loader’ which is provided by the computer manufacturer.
  • Then the computer loads in the Operating System in boot drive to the RAM (Random Access Memory)
  • Once this is performed the Operating System takes over the control of the computer and displays a user interface to the user.

This whole process is called booting which means that an Operating System is loaded into the RAM (main memory).

Software is a set of instructions given to the computer to perform some activity using a computer. There are many types of software. They can be broadly classified as follows:
System Software

Operating System
The Operating System provides for the user to utilize the functions of a computer by managing the hardware and software in it. The image 5.2 below depicts how the system software and application software interact with the hardware. 

Utility Software

These are used to manage and analyze the software in the computer. The utility software differ from the application software in their complexity and operational activities. Utility software helps in managing the resources of the computer. However, the application software function in different to the utility software. There are many utility software which dedicated to perform certain functions. Some of them are mentioned below
  • Anti -Virus Software
  • Disk Formatting
  • Games
  • Player
Language Translators

A computer program (software) is made up by using a set of instruction codes. These instructions are written in high level languages which are very close to the human languages. These high level languages are translated into machine language (i.e 0’s and 1’s) which are understood by the computer by language translators. assembler, compiler and interpreter are examples for language translators.

Application Software

The application software which runs on the Operating System is used to carry out computer based activities of the user such as creating documents, mathematical functions, data entry and, computer games.
  • MS Word
  • Fir Fox
  • Far Cry 5 Game 
  • Photoshop
  • VLC Player
  • Notepad++

Network Topology 
Network topology refers to how various nodes, devices, and connections on your network are physically or logically arranged in relation to each other. Think of your network as a city, and the topology as the road map. Just as there are many ways to arrange and maintain a city—such as making sure the avenues and boulevards can facilitate passage between the parts of town getting the most traffic—there are several ways to arrange a network. Each has advantages and disadvantages and depending on the needs of your company, certain arrangements can give you a greater degree of connectivity and security.

There are two approaches to network topology: physical and logical. Physical network topology, as the name suggests, refers to the physical connections and interconnections between nodes and the network—the wires, cables, and so forth. Logical network topology is a little more abstract and strategic, referring to the conceptual understanding of how and why the network is arranged the way it is, and how data moves through it.

Star Topology 
A star topology, the most common network topology, is laid out so every node in the network is directly connected to one central hub via coaxial, twisted-pair, or fiber-optic cable. Acting as a server, this central node manages data transmission—as information sent from any node on the network has to pass through the central one to reach its destination—and functions as a repeater, which helps prevent data loss.

BUS Topology 
A transport topology situates all the gadgets on a system along a solitary link running a solitary way from one finish of the system to the next—which is the reason it's occasionally called a "line topology" or "spine topology." Data stream on the system likewise follows the course of the link, moving in one heading.

Ring Topology 
Ring topology is the place hubs are organized around (or ring). The information can go through the ring system in it is possible that one course or the two headings, with every gadget having precisely two neighbors.

Tree Topology 
The tree topology structure gets its name from how the focal hub works as a kind of trunk for the system, with hubs broadening outward in a branch-like style. In any case, where every hub in a star topology is legitimately associated with the focal center point, a tree topology has a parent-youngster chain of importance to how the hubs are associated. Those associated with the focal center point are associated directly to different hubs, so two associated hubs just offer one shared association. Since the tree topology structure is both very adaptable and versatile, it's frequently utilized for wide region systems to help many spread-out gadgets.

Mash Topology 
A work topology is a many-sided and expound structure of point-to-point associations where the hubs are interconnected. Work systems can be full or fractional work. Fractional work topologies are generally interconnected, with a couple of hubs with just a few associations, while full-work typologies are—shock!— completely interconnected.

Types of Network
A PC arrange is a gathering of PCs associated with one another through a transmission medium, for example, link, wire and so on. In this guide, we will talk about the sorts of PC arranges in detail. There are mainly three types of computer networks based on their size:

  • Local Area Network (LAN)
  • PAN(Personal Area Network)
  • Metropolitan Area Network (MAN)
  • Wide area network (WAN)

Local Area Network (LAN)
LAN is extended as Local Area Network where the pool of PCs are connected to one another in restricted extents like condo and office premise. This PC arrange associates the pool of PCs by means of a specialized gadget like coaxial link, switches and switches and turned sets.

It is accessible requiring little to no effort and worked with inexpensively accessible equipment, for example, Ethernet links, arrange connectors, and center points. Here the exchange pace of information is high with insignificant reaction time. This is an exceptionally protected system less inclined to hacks and information misfortune.

PAN(Personal Area Network) 
Dish is extended as Personal Area Network is arranged in an individual in scope of around ten meters and is generally utilized for associating web run for individual use. It has the inclusion range to thirty meters. Individual hardware incorporates work area, PC, cell phones, game stations, electronic devices, and music players.

Metropolitan Area Network (MAN) 
MAN arrange covers bigger zone by associations LANs to a bigger system of PCs. In Metropolitan region organize different Local region systems are associated with one another through phone lines. The size of the Metropolitan region arrange is bigger than LANs and littler than WANs(wide region organizes), a MANs covers the bigger zone of a city or town.

Wide area network (WAN)
Wide zone arrange gives significant distance transmission of information. The size of the WAN is bigger than LAN and MAN. A WAN can cover nation, mainland or even an entire world. Web association is a case of WAN. Different instances of WAN are portable broadband associations, for example, 3G, 4G and so forth.

A network, in computing, is a cluster of 2 or more devices which will communicate. In follow, a network is comprised of variety of various pc systems connected by physical and/or wireless connections. the dimensions will vary from one computer sharing out basic peripherals to huge data centres set round the World, to the net itself. regardless of scope, all networks enable computers and/or people to share information and resources.

Advantages of networks

1.      Sharing devices such as printers saves money.
2.      Site (software) licences are likely to be cheaper than buying several standalone licences.
3.      Files can easily be shared between users.
4.      Network users can communicate by email and instant messenger.
5.      Security is good - users cannot see other users' files unlike on stand-alone machines.
6.      Data is easy to backup as all the data is stored on the file server.

Disadvantages of networks

1.      Purchasing the network cabling and file servers can be expensive.
2.      Managing a large network is complicated, requires training and a network manager usually needs to be employed.
3.      If the file server breaks down the files on the file server become inaccessible. Email might still work if it is on a separate server. The computers can still be used but are isolated.
4.      Viruses can spread to other computers throughout a computer network.
5.      There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse, e.g. a firewall.
Computer network devices
There should be two or more computers to build a computer network. Connection devices used to connect computers with each other. Here is the common hardware network device list:
  1. Hub
  2. Routers
  3. Switches
  4. Firewall
  5. Bridges
  6. Modem 
  7. Access Point
  8. Content Filter
  9. Load Ba lancer
  10. Packet Sharpe
  11. VPN concentration
A hub, within the context of networking, may be a hardware device that relays communication information. A hub sends information packets (frames) to any or all devices on a network, in spite of any raincoat addresses contained within the information packet.

Router could be a network layer (Layer 3) of the OSI reference model device meaning it will connect multiple laptop networks via wired or wireless connections. Network router will receive, analyze, perform the traffic directive functions and forwards information packet from one network to its destination node. A router could be a device that forwards packets between networks by process the routing data enclosed within the packet.

A switch, within the context of networking could be a high-speed device that receives incoming information packets and redirects them to their destination on an area a neighborhood area network (LAN). A LAN switch operates at the info link layer (Layer 2) or the network layer of the OSI Model and, per se it will support all kinds of packet protocols.
Essentially, switches area unit the traffic cops of a straightforward native space network.

A firewall will be a hardware or software package device. A hardware firewall may be a unit that's connected between the network and also the device for connecting to the web. A software package firewall may be a program that's put in on the pc with the web association

Bridges square measure want to connect 2 or a lot of hosts or network segments along. the fundamental role of bridges in specification is storing and forwarding frames between the various segments that the bridge connects. They use hardware Media Access management (MAC) addresses for transferring frames. By viewing the Mack address of the devices connected to every section, bridges will forward the information or block it from crossing. Bridges may be wont to connect 2 physical local area networks into a bigger logical LAN.

Modems (modulators-demodulators) area unit want to transmit digital signals over analog phone lines. Thus, digital signals area unit born-again by the electronic equipment into analog signals of various frequencies and transmitted to an electronic equipment at the receiving location. The receiving electronic equipment performs the reverse transformation and provides a digital output to a tool connected to an electronic equipment, typically a laptop. The digital information is typically transferred to or from the electronic equipment over a serial line through AN business customary interface, RS-232. several phone firms supply phone line services, and lots of cable operators use modems as finish terminals for identification and recognition of home and private users. Modems work on each the Physical and link layers.

Load Balance
A hardware load-balancing device (HLD), also known as a layer 4-7 router, is a physical unit that directs computers to individual servers in a network, based on factors such as server processor utilization, the number of connections to a server, or the overall server performance.

Firewall/ Client/ Server network
A firewall is a system designed to prevent unauthorized access to or from a private network. You can implement a firewall in either hardware or software form, or a combination of both. Firewalls prevent unauthorized internet users from accessing private networks connected to the internet, especially intranets.

A client is a piece of computer hardware or software that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network

In computing, a server is a computer program or a device that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model, and a single overall computation is distributed across multiple processes or devices

The following are the basic components that are needed for data communication.

  • Sender / Source – the person or the object which sends data
  • Medium – medium used to transmit data (telephone wires / wireless)
  • Receiver/ destination – the person or the object which receives data
Data Transmission Modes
There are several modes of data transmission between sender and receiver. 

Simplex Mode
Data is transmitted from the sender to the receiver only. Getting print outs, watching television, and listening to radio can be given as examples

Half- duplex Mode
Here, data is transmitted to one direction at a time. This means after data is transmitted from sender / source to the receiver, the receiver can transmit data back to the sender / source. Browsing internet to get information and walkie-talkie used by security forces can be given as examples.

Full Duplex Mode
Data is transmitted to both sides at the same time is called Full duplex. Telephone conversation is an example for full duplex mode communication.

Data Transmission Media
This is another important feature when creating connections among systems. There are two types of data transmission medium. Those are called Guided/Wired and Unguided/Wireless. The following are some examples.

Guided / Wired
If the medium used for data transmission is a physical medium, it is called guided or wired.

Twisted Pair
  1. Unshielded Twisted Pair (UTP)
The twisted copper wire pairs used for telephone connections. These are very flexible and low-priced. However, it is difficult to transmit data for a long distance through UTP wires. It is suitable for maximum of 100 meters.  
    1. Shielded Twisted Pair (STP) 
    STP is a better quality and secure data transmission medium. However it is expensive.

    Coaxial Cable

    Fiber Optics cable 

    Unguided/Wireless Media
    Data is transmitted as signal through the air without using physical medium is called unguided/wireless media

    Radio waves
    Data transmission is performed using radio waves. Wifi and Bluetooth are examples for radio waves based communication.

    Microwaves travel in a linear mode. Transmission center is positioned facing each other. The distance between centers are decided based on geographical factor of the area. Microwaves are used in Satellite communication to transmit data as transponders. Satellite centers, which are positioned in the sky above 36000 km, capture data transmitted as microwaves through satellite towers positioned in the Earth and then transmit the data back to the required tower. Using this method, data can be transmitted to any distance. This is also used in internet communication. 

    Infrared data transmission is used in TV remote controllers, wireless keyboards and mouse etc. 

    Computer Ports 
    The interfaces which connect computer with its devices or with other computers are called ports. (Figure 2.48) Ports are positioned in the front or back of the computer. There are symbols to identify posts. All the ports are connected to the motherboard.

    1. PS/2 Port
    Used to connect the keyboard and the mouse to the computer system. The purple port is for the keyboard and the green port is for the mouse. (Figure 2.50) However, USB port is mostly used today to connect the keyboard and the mouse to the computer system.

    2. Parallel Port
    Used to connect the printer to the computer system. This consists of 25 holes. However, USB port is mostly used today to connect printers to computer systems.

    3. HDMI (High - Definition Multimedia
    Interface) port This port can be seen especially in laptops. (Figure 2.52) It connects the monitor, multimedia projector, digital TVs, and digital speakers to the computer.

    4. RJ 45 Port
    This port connects computer of a computer network to the network router, network switch.

    5. Audio Ports/ Jacks
    This port connects audio media like microphones, speakers and head phones to the computer system.

    • Blue – Line In
    • Green – Line Out, Head Phone
    • Pink – Microphone

    6. USB (Universal Serial Bus Port)
    This port is used to connect many types of input and output devices to the computer.

    7. Video port - VGA (Video Graphics Adapter)
    This is also called the Graphic Port. This connects the monitor, or multimedia projector to the computer system. The port consists of 15 holes.

    8. Serial port
    This port connects devices such as modem to the computer. Today, USB port is used instead of the serial port


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