Operating Systems and Computer Networks - UNIT – IV

UNIT – IV

1. Operating Systems 

2. Components of Operating System

3. Functions of Operating System

4. Types of Operating System; Linux/Dos/Windows. 

5. Computers and Communication: Single user, multi-user, workstation, and client server systems.

 6. Computer networks, Network protocols. LAN, WAN, Services offered by Internet.   

1. An operating system is a program that acts as an intermediary between a user of a computer and the computer hardware.

 

2. Components of Operating System

The components of an operating system play a key role to make a variety of computer system parts work together. There are the following components of an operating system, such as:

1. Process Management
2. File Management
3. Network Management
4. Main Memory Management
5. Secondary Storage Management
6. I/O Device Management
7. Security Management
8. Command Interpreter System

3. Important functions of an operating System: 

1. Security – 
   The operating system uses password protection to protect user data and similar other techniques. it also prevents unauthorized access to programs and user data. 
    
2. Control over system performance – 
   Monitors overall system health to help improve performance. records the response time between service requests and system response to having a complete view of the system health. This can help improve performance by providing important information needed to troubleshoot problems. 
    
3. Job accounting – 
   Operating system Keeps track of time and resources used by various tasks and users, this information can be used to track resource usage for a particular user or group of users. 
    
4. Error detecting aids – 
   The operating system constantly monitors the system to detect errors and avoid the malfunctioning of a computer system. 
    
5. Coordination between other software and users – 
   Operating systems also coordinate and assign interpreters, compilers, assemblers, and other software to the various users of the computer systems. 
    
6. Memory Management – 
   The operating system manages the Primary Memory or Main Memory. Main memory is made up of a large array of bytes or words where each byte or word is assigned a certain address. Main memory is fast storage and it can be accessed directly by the CPU. For a program to be executed, it should be first loaded in the main memory. 
7. Processor Management – 
   In a multi-programming environment, the OS decides the order in which processes have access to the processor, and how much processing time each process has. This function of OS is called process scheduling. An Operating System performs the following activities for processor management. 

   Keeps track of the status of processes. The program which performs this task is known as a traffic controller. Allocates the CPU that is a processor to a process. De-allocates processor when a process is no more required. 
    

8. Device Management – 
   An OS manages device communication via their respective drivers. It performs the following activities for device management. Keeps track of all devices connected to the system. designates a program responsible for every device known as the Input/Output controller. Decides which process gets access to a certain device and for how long. Allocates devices in an effective and efficient way. Deallocates devices when they are no longer required. 
    
9. File Management – 
   A file system is organized into directories for efficient or easy navigation and usage. These directories may contain other directories and other files. An Operating System carries out the following file management activities. It keeps track of where information is stored, user access settings and status of every file, and more…

4. Types of Operating System; Linux/Dos/Windows. 

DOS: DOS stands for Disk Operating System, which is an operating system that was popular till 1995 in IBM PCs. It is a single-tasking OS i.e., it can perform one task at a time. It is based on a command-line interface where one has to provide instructions to the computer in the command form. It runs from hard disks, floppy disks, or any other storage devices and thus provides an environment for the execution of programs. It occupies less memory. To use more than 64kb of memory, memory extenders were used, which older Windows used to use more memory. 

Windows: Windows is a product of Microsoft. It is an operating system with various versions, Windows 11 being the latest version. It is a Graphics-Based user interface. Users give commands through clicking or choosing icons and images with the help of a mouse, keyboard, or touchscreen to the computer. 

Linux : Linux is a freely distributed multitasking and multi-user operating system that behaves like UNIX. It is the best known and most commonly used open-source operating system. It is a cross-platform operating system based on UNIX that can be installed on PCs and laptops.

5. Computers and Communication: Single user, multi-user, workstation, and client server systems

Single User Operating System

A single-user operating system is a type of operating system developed and intended for use on a computer or similar machine that will only have a single user at any given time. This type of OS is typically used on devices like wireless phones and two-way messaging devices.

The operating system is responsible for handling many different tasks and is typically one of the most important programs used on a computer. It manages memory usage and other resources, hardware connectivity and the proper execution of other applications. A single task operating system can only run one program or application at a time.

Multi-user operating system 
A multi-user operating system is an operating system that permits several users to access a single system running to a single operating system. These systems are frequently quite complex, and they must manage the tasks that the various users connected to them require. Users will usually sit at terminals or computers connected to the system via a network and other system machines like printers. A multi-user operating system varies from a connected single-user operating system in that each user accesses the same operating system from different machines.

Client and server networking model

• A client and server networking model is a model in which computers such as servers provide the network services to the other computers such as clients to perform a user based tasks. This model is known as client-server networking model.

• The application programs using the client-server model should follow the given below strategies.

• An application program is known as a client program, running on the local machine that requests for a service from an application program known as a server program, running on the remote machine.

• A client program runs only when it requests for a service from the server while the server program runs all time as it does not know when its service is required.

• A server provides a service for many clients not just for a single client. Therefore, we can say that client-server follows the many-to-one relationship. Many clients can use the service of one server.

• Services are required frequently, and many users have a specific client-server application program. For example, the client-server application program allows the user to access the files, send e-mail, and so on. If the services are more customized, then we should have one generic application program that allows the user to access the services available on the remote computer.

Client

A client is a program that runs on the local machine requesting service from the server. A client program is a finite program means that the service started by the user and terminates when the service is completed.

Server

A server is a program that runs on the remote machine providing services to the clients. When the client requests for a service, then the server opens the door for the incoming requests, but it never initiates the service.

6. Computer networks, Network protocols

 LAN, WAN, Services offered by Internet 

A computer network is a set of computers sharing resources located on or provided by network nodes. 

Network Protocols are a set of rules governing exchange of information in an easy, reliable and secure way.

. It permits connected devices to communicate with each other, irrespective of internal and structural differences.

Types of protocols

The protocols can be broadly classified into three major categories-

1. Communication
2. Management
3. Security

1. HTTP: It is a layer 7 protocol that is designed for transferring a hypertext between two or more systems. HTTP works on a client-server model, most of the data sharing over the web are done through using HTTP.
2. TCP: It lay-outs a reliable stream delivery by using sequenced acknowledgment. It is a connection-oriented protocol i.e., it establishes a connection between applications before sending any data. It is used for communicating over a network. It has many applications such as emails, FTP, streaming media, etc.
3. FTP: FTP is a Client/server protocol that is used for moving files to or from a host computer, it allows users to download files, programs, web pages, and other things that are available on other services.
4. HTTPS: It is the secured version of HTTP; this protocol ensures secure communication between two computers where one sends the request through the browser and the other fetches the data from the webserver.

 Local Area Network (LAN): LAN is a group of network devices that allow communication between connected devices. The private ownership has the control over the local area network rather than the public. 

 It covers the smallest area such as College, School Hospital and so on. 

Wide Area Network (WAN): WAN covers a large area than LAN as well as MAN such as Country/Continent etc. WAN is expensive and should or might not be owned by one organization. PSTN or Satellite medium is used for wide area networks. 

Internet services

To access/exchange a large amount of data such as software, audio clips, video clips, text files, other documents, etc., we need internet services. You must use an Internet service to connect to the Internet. Data can be sent from Internet servers to your machine via Internet service. Some of the commonly used internet services are :

• Communication Services
• Information Retrieval Services
• File Transfer
• World Wide Web Services
• Web Services
• Directory Services
• Automatic Network Address Configuration
• Network Management Services
• Time Services
• Usenet
• NewsGroup
• Ecommerce