Introduction to Operating Systems and Process

 

 Introduction to Operating Systems

1. Operating System

• Definition: An operating system (OS) is a collection of software that manages  computer hardware and software resources. 
• Role: The OS acts as an intermediary between users and the computer            hardware, enabling user interaction through applications.

2. Supervisor & User Mode

1. Supervisor Mode (Kernel Mode):

• Definition: Kernel mode is a high-privilege state that allows direct access to hardware and system resources
• Full access to all hardware and system resources.
• Can execute any instruction and access any memory address.
• Critical for core OS functions like memory management and process scheduling.

1. User Mode:

• Limited access to system resources, preventing direct hardware manipulation.
• Ensures stability and security by restricting user applications from interfering with the OS.

3. Multiprogramming and Multiprocessing Systems

Multiprogramming:

• Multiple programs loaded in memory, enabling the CPU to switch between them to maximize CPU utilization.
• Reduces idle time by keeping the CPU busy with different tasks.

Multiprocessing:

• Involves multiple CPUs or cores that can execute multiple processes simultaneously.
• Enhances performance, as processes can run in parallel, improving system responsiveness.

4. OS Structure

Monolithic Structure:

• All OS services run in kernel mode within a single large block of code.
• Simple and efficient but less flexible and harder to maintain.
• Layered Structure:
• Divides the OS into layers, each with specific responsibilities (e.g., hardware layer, kernel layer, user interface layer).
• Improves modularity and makes debugging easier.

Microkernel:

• Minimal core kernel providing basic services (e.g., communication, basic scheduling).
• Other services (e.g., file systems, drivers) run in user space, improving stability.
• Modules:
• Dynamic loading of kernel modules allows the OS to extend its functionality without a reboot.
• Facilitates easier updates and system enhancements.

5. System Calls

• Definition: System calls are interfaces through which user applications request services from the OS.
• Examples:
• read(): Reads data from a file.
• write(): Writes data to a file.
• open(): Opens a file descriptor.
• close(): Closes a file descriptor.
• Importance: Allows user-level programs to communicate with the OS and access hardware resources securely.

6. Functions of OS

• Process Management: Handling process creation, scheduling, and termination.
• Memory Management: Allocating and managing memory space for processes.
• File System Management: Managing file operations and directory structures.
• Device Management: Controlling and coordinating hardware devices.
• User Interface: Providing command-line or graphical interfaces for user interaction.

7. Evolution of OSs

Early Systems:

• Batch processing systems that executed jobs sequentially.
• Simple monolithic kernels without multitasking.
• Time-sharing Systems:
• Allowed multiple users to access the system simultaneously.
• Introduced concepts of multitasking and user interaction.
• Personal Computer Operating Systems:
• Emergence of systems like MS-DOS, Windows, and macOS.
• User-friendly interfaces and support for multitasking.

Modern OS:

• Advanced OS like Linux, Android, and cloud-based systems.
• Focus on security, networking, and mobile computing.
• Process Management

Process Management

1. Process Concept

• Definition: A process is an active program in execution, consisting of program code, current activity, and the resources allocated to it (like memory, I/O devices).
• Components:
• Program Counter: Indicates the next instruction to be executed.
• Stack: Contains temporary data (e.g., function parameters, return addresses).
• Data Section: Contains global variables.

2. Life Cycle of a Process

• New: The process is being created.
• Ready: The process is in memory and waiting to be assigned to the CPU.
• Running: The process is currently executing on the CPU.
• Waiting: The process is waiting for an event to occur (e.g., I/O completion).
• Terminated: The process has completed execution or has been killed.

3. Process Control Block (PCB)

• Definition: A PCB is a data structure maintained by the OS that contains information about a process.
• Components:
• Process ID (PID): Unique identifier for the process.
• Process State: Current state of the process (e.g., running, waiting).
• Program Counter: Address of the next instruction to execute.
• CPU Registers: Current values of CPU registers.
• Memory Management Information: Information about memory allocated to the process.
• I/O Status Information: List of I/O devices allocated to the process.

4. Operations on Processes

• Creation: Involves allocating resources and initializing the PCB (e.g., using fork() in UNIX).
• Scheduling: Determining which process to execute based on scheduling algorithms (e.g., Round Robin, Shortest Job First).
• Termination: Releasing resources when a process finishes or is forcibly terminated.

5. Co-operating and Independent Processes

Independent Processes:

• Do not affect or get affected by other processes.
• Operate in isolation.
• Co-operating Processes:
• Share data and resources with other processes.
• Require synchronization to avoid conflicts (e.g., using semaphores or mutexes).

6. Process States

• Ready: The process is ready to run but waiting for CPU time.
• Blocked (Waiting): The process cannot continue until an event occurs (e.g., I/O operation completes).
• Running: The process is actively executing on the CPU.

7. Operations on Processes

• Fork: Creates a new process (child process) that is a duplicate of the current process.
• Exec: Replaces the current process's memory space with a new program, effectively running a different program.
• Wait: A process can wait for another process to finish, preventing it from proceeding until that event occurs.
• Signal: A process can send a signal to another process to notify it of an event (e.g., completion of I/O).

8. Process Management in UNIX

• UNIX employs a rich set of process management features, including:
• Fork and Exec for creating and executing processes.
• Signals for inter-process communication and synchronization.
• Process States management via the scheduler.
• Job Control to manage foreground and background processes.

9. Process Control Block (PCB) in UNIX

• Similar to the general PCB definition, the UNIX PCB holds essential information for managing processes, ensuring efficient execution and resource allocation.

                 ✋ Thank You For Visiting✋