UNIT 2 : Operating system And Computer Network.

 

Operating System (OS)

Definition:

An Operating System (OS) is a system software that manages computer hardware, software resources, and provides common services for computer programs. It acts as an intermediary between computer hardware and the user, facilitating efficient execution of programs.

Functions of an Operating System:

1. Process Management:

   • The OS manages processes in the system, including process scheduling, execution, and termination.
   • It ensures the smooth operation of all processes by allocating CPU time and resources.

2. Memory Management:

   • The OS manages the computer’s memory, allocating and deallocating memory spaces as needed by processes.
   • It also ensures the optimal use of memory and handles virtual memory.

3. File System Management:

   • The OS organizes and manages files on storage devices.
   • It provides access control, storage allocation, and file protection.

4. Device Management:

   • The OS controls hardware devices such as printers, disk drives, and display monitors.
   • It manages input/output operations and ensures that devices are used efficiently.

5. Security and Access Control:

   • The OS provides security features such as authentication (user login), encryption, and access control to prevent unauthorized access.

6. User Interface (UI):

   • The OS provides an interface for users to interact with the system (via command-line interface (CLI) or graphical user interface (GUI)).

7. Resource Allocation:

   • The OS allocates resources such as CPU time, memory, and peripheral devices to different tasks based on priorities.

Types of Operating Systems:

1. Batch Operating Systems:

   • No direct interaction between the user and the computer. Jobs are grouped into batches and processed sequentially.

2. Time-Sharing Operating Systems:

   • Multiple users share system resources simultaneously. The system switches between users quickly to give the illusion of concurrent execution.

3. Real-Time Operating Systems (RTOS):

   • These systems are designed to process data and perform tasks in real-time with strict timing constraints (e.g., in embedded systems, industrial control systems).

4. Distributed Operating Systems:

   • These systems manage a group of independent computers and present them as a unified system. They enable sharing of resources across multiple computers.

5. Network Operating Systems (NOS):

   • These OSs manage network resources and services, such as file sharing, device sharing, and security within a network.

6. Multitasking/Multiprogramming Operating Systems:

   • These systems allow multiple processes to run at the same time by rapidly switching between them.

Classification of Operating Systems:

• Single-tasking vs. Multi-tasking:

  • Single-tasking OS allows one process at a time, while multi-tasking allows multiple processes to run simultaneously.

• Single-user vs. Multi-user:

  • Single-user OS is designed for one user (e.g., Windows), while multi-user OS supports multiple users simultaneously (e.g., Linux, Unix).

• Monolithic vs. Microkernel:

  • Monolithic kernels have a single large kernel that handles everything, while microkernels provide minimal functionality and depend on other services for additional features.

Elements of Command-Based and GUI-Based Operating Systems:

1. Command-Based OS (CLI – Command Line Interface):

   • Definition: Users interact with the OS by typing commands in a text-based interface.

   • Elements:

     • Command Interpreter: It processes user commands (e.g., Bash in Linux).
     • File System Navigation: The user needs to type commands to access files and directories.
     • Text-based Input and Output: The interaction happens through text input and output.

   • Advantages:

     • More control over the system.
     • Faster for experienced users.

   • Examples: MS-DOS, Unix, Linux (Terminal).

2. GUI-Based OS (Graphical User Interface):

   • Definition: Users interact with the OS using visual elements such as icons, buttons, and windows.
   • Elements:
     • Windows: Rectangular areas on the screen that display information or run programs.
     • Icons: Graphical representations of files, programs, or actions.
     • Menus: A list of options that can be selected by the user.
     • Pointing Devices (Mouse/Touchscreen): Used to navigate through the OS and interact with visual elements.
   • Advantages:
     • Easier for beginners and non-technical users.
     • Provides a more intuitive and visually appealing interface.
   • Examples: Windows, macOS, Linux (with a GUI environment like GNOME or KDE).

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Computer Network

Overview:

A computer network is a system of interconnected devices (such as computers, servers, and routers) that can communicate and share resources (files, printers, internet access, etc.) via wired or wireless connections. Networks enable the exchange of data and information between devices across various distances.

Types of Computer Networks:

1. Local Area Network (LAN):

   • Definition: A network confined to a small geographic area, such as a single building or office.
   • Characteristics:
     • High data transfer speed (typically 100 Mbps to 10 Gbps).
     • Typically uses Ethernet cables or Wi-Fi for connections.
     • Used to share resources like files, printers, and internet access.
   • Examples: Home networks, office networks.

2. Wide Area Network (WAN):

   • Definition: A network that covers a large geographic area, often connecting multiple LANs across cities or countries.
   • Characteristics:
     • Can span long distances (city-wide, country-wide, or global).
     • Typically uses leased lines, satellite links, or the internet for communication.
     • Slower data transfer speeds compared to LANs.
   • Examples: The internet, corporate networks across cities.

3. Metropolitan Area Network (MAN):

   • Definition: A network that spans a city or a large campus, larger than a LAN but smaller than a WAN.
   • Characteristics:
     • Covers a geographical area of 5 to 50 kilometers.
     • Often used to connect several LANs within a specific region.
     • Can be managed by a single organization or by a service provider.
   • Examples: City-wide Wi-Fi, cable TV networks.

Data Communication:

Data communication refers to the process of transferring data between devices over a communication medium (wired or wireless). Key elements include:

1. Sender: The device that sends the data.
2. Receiver: The device that receives the data.
3. Transmission Medium: The physical path (cables, air) used for data transfer.
4. Protocol: A set of rules that govern the communication between devices.

Common communication mediums include:

• Wired: Ethernet cables, fiber optics.
• Wireless: Wi-Fi, Bluetooth, radio waves.

Topologies:

Network topology refers to the physical or logical arrangement of devices in a network.

1. Bus Topology:

   • A single central cable (the bus) connects all devices in the network.
   • Cheap and easy to install but suffers from performance degradation as more devices are added.

2. Star Topology:

   • All devices are connected to a central device (e.g., switch or router).
   • Provides better performance and easier fault isolation but depends on the central device.

3. Ring Topology:

   • Devices are connected in a circular fashion, with data circulating in one direction.
   • Performs well but is vulnerable to network failure if one connection is broken.

4. Mesh Topology:

   • Every device is connected to every other device in the network.
   • Provides high redundancy and reliability but is expensive and complex to set up.

5. Tree Topology:

   • A hybrid of bus and star topologies, where groups of star-configured devices are connected to a central bus.
   • Suitable for large networks but can be difficult to maintain.

6. Hybrid Topology:

   • Combines two or more topologies to take advantage of their respective strengths.
   • Can be complex but is flexible and scalable.

Each topology has its own advantages and disadvantages, and the choice of topology depends on the network's size, requirements, and budget.