Operating System: Core Functions

• An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs
• It acts as an intermediary between the user and the hardware, providing a platform for running applications
• The OS is a crucial component of a computer system, managing everything from the CPU and memory to storage devices and peripherals

Core Functions

• Resource Management: The OS allocates and manages system resources such as CPU time, memory, and I/O devices to ensure efficient and fair utilization among competing processes
• Process Management: It creates, schedules, and terminates processes, allocating resources and coordinating their execution
• Memory Management: The OS manages the allocation and deallocation of memory to different processes, preventing them from interfering with each other and optimizing memory usage
• File System Management: It organizes files and directories on storage devices, providing a hierarchical structure and mechanisms for accessing and manipulating files
• Device Management: The OS provides drivers and interfaces for interacting with hardware devices, allowing applications to use them without needing to know the specific details of their operation
• User Interface: It provides a user interface (UI), which can be a command-line interface (CLI) or a graphical user interface (GUI), for users to interact with the system
• Security: The OS provides security mechanisms to protect the system from unauthorized access and malicious software

Types of Operating Systems

• Batch OS: Executes jobs in batches without user interaction
• Time-Sharing OS: Allows multiple users to share the computer simultaneously by allocating CPU time slices to each user
• Real-Time OS (RTOS): Designed for applications with strict timing requirements, such as industrial control systems and embedded systems
• Distributed OS: Manages a network of computers as a single system, allowing resources to be shared and tasks to be distributed across multiple machines
• Embedded OS: Designed for embedded systems, such as mobile phones, appliances, and automobiles, with limited resources and specific functionalities
• Mobile OS: Specifically designed for mobile devices, such as smartphones and tablets, with features like touch screen support, app stores, and wireless connectivity

Key Concepts

• Kernel: The core of the operating system, responsible for managing the system's resources and providing services to applications
• Processes: An instance of a program being executed, with its own memory space and resources
• Threads: A lightweight unit of execution within a process, allowing for concurrent execution of multiple tasks within the same process
• Memory address space: A range of memory addresses that a process can access
• Virtual memory: A technique that allows processes to use more memory than is physically available by swapping data between RAM and secondary storage
• File system: A hierarchical structure for organizing and storing files on a storage device
• Device drivers: Software that allows the operating system to communicate with hardware devices
• System calls: A mechanism for applications to request services from the operating system kernel
• Shell: A command-line interpreter that allows users to interact with the operating system

Memory Management Techniques

• Contiguous Memory Allocation: Allocates a contiguous block of memory to each process
• Paging: Divides memory into fixed-size blocks called pages, allowing non-contiguous allocation of memory to processes
• Segmentation: Divides memory into variable-size blocks called segments, allowing logical grouping of related code and data
• Virtual Memory: Allows processes to use more memory than is physically available by swapping data between RAM and secondary storage (e.g., hard disk)
• Demand Paging: Loads pages into memory only when they are needed, reducing memory usage and improving performance
• Page Replacement Algorithms: Algorithms used to decide which page to remove from memory when a new page needs to be loaded (e.g., FIFO, LRU, Optimal)

Process Management

• Process States: A process can be in various states, such as new, ready, running, waiting, and terminated
• Process Control Block (PCB): A data structure that contains information about a process, such as its ID, state, memory allocation, and CPU registers
• Process Scheduling: Algorithms used to determine which process to run next (e.g., FCFS, SJF, Priority, Round Robin)
• Context Switching: The process of saving the state of one process and loading the state of another process, allowing the CPU to switch between processes
• Inter-Process Communication (IPC): Mechanisms for processes to communicate with each other, such as pipes, message queues, shared memory, and sockets
• Deadlock: A situation where two or more processes are blocked indefinitely, waiting for each other to release resources

File System Management

• File Attributes: Information about a file, such as its name, size, type, creation date, and access permissions
• File Operations: Common operations performed on files, such as create, read, write, delete, and rename
• Directory Structure: A hierarchical structure for organizing files into directories (folders)
• File System Types: Different types of file systems, such as FAT, NTFS, ext4, and HFS+, each with its own features and limitations
• Disk Scheduling Algorithms: Algorithms used to optimize the order in which disk I/O requests are serviced (e.g., FCFS, SSTF, SCAN, C-SCAN)

Security Features

• User Authentication: Verifying the identity of users through usernames, passwords, and other authentication methods
• Access Control: Restricting access to system resources based on user identity and permissions
• Encryption: Encoding data to protect it from unauthorized access
• Firewalls: Software or hardware that filters network traffic to prevent unauthorized access to the system
• Intrusion Detection Systems (IDS): Systems that monitor network traffic and system activity for malicious behavior
• Virus Protection: Software that detects and removes viruses and other malware

Virtualization

• Virtual Machine (VM): A software-based emulation of a computer system, allowing multiple operating systems to run concurrently on a single physical machine
• Hypervisor: Software that creates and manages virtual machines

Types of Virtualization:

- Hardware Virtualization: Hypervisor runs directly on the hardware
- Hosted Virtualization: Hypervisor runs on top of an existing operating system

• Containerization: A lightweight form of virtualization that isolates applications and their dependencies in containers, sharing the host OS kernel
• Docker: A popular containerization platform

System Calls

• System calls provide an interface between user-level processes and the operating system kernel
• They allow processes to request services from the kernel, such as accessing hardware, creating processes, and managing files

Examples of system calls:

- `read()`: Reads data from a file
- `write()`: Writes data to a file
- `open()`: Opens a file
- `close()`: Closes a file
- `fork()`: Creates a new process
- `exec()`: Executes a new program
- `exit()`: Terminates a process

Booting Process

• The booting process is the sequence of steps that a computer takes to start up and load the operating system

Steps in the booting process:

- BIOS/UEFI initialization: The BIOS/UEFI firmware initializes the hardware and performs a power-on self-test (POST)
- Bootloader: The bootloader is loaded from the boot device and is responsible for loading the operating system kernel
- Kernel loading: The kernel is loaded into memory and begins execution
- Initialization: The kernel initializes the system and starts system services
- Login: The user is prompted to log in