Operating Systems Concepts - Unit 1 Introduction

Operating Systems Concepts

• Operating systems (OS) act as an intermediary between hardware and software
• Fundamental functions of an OS include resource management, process management, memory management, file system management, device management, user interfaces, security, error handling, and networking.

Unit 1 - Introduction

• Introduction: An OS is a fundamental component of a computer system that acts as an intermediary between hardware and user or application software.
• Resource Management: The OS manages hardware resources (CPU, memory, storage, I/O). It allocates these resources to programs and ensures efficient use.
• Process Management: The OS allows for concurrent execution of multiple programs (processes). It provides mechanisms for inter-process communication and ensures they run without interfering.
• Memory Management: The OS manages system memory by ensuring each program has enough space and prevents interference between processes. Techniques like virtual memory are used to provide more memory than physically available.
• File System Management: The OS manages files and directories, allowing users to store, retrieve, and organize data efficiently. Permissions and access control are managed by the OS.
• Device Management: The OS controls the interaction between software and hardware devices through device drivers.
• User Interface: The OS provides an interface for users to interact with the system (command line or graphical user interface).
• Security and Access Control: The OS enforces security policies, user authentication, access controls, and protects the system from unauthorized access and data breaches.
• Error Handling and Exceptions: The OS provides mechanisms for handling errors and exceptions, preventing system crashes due to software bugs.
• Networking: Modern OSs include integrated networking capabilities for communication over networks.
• Task Scheduling: The OS uses algorithms to determine the order of process execution, ensuring fair allocation of CPU time and system responsiveness.

Unit 2 - Process Synchronization: Mutual Exclusion

• Mutual Exclusion: A fundamental concept in process synchronization, ensuring only one process or thread can access a critical section (shared resource/code) at a time.
• Objective: Coordinate process access to shared resources and prevent race conditions.
• Techniques for Achieving Mutual Exclusion:
  • Locks (mutexes): Used to protect critical sections.
  • Semaphores: More versatile synchronization objects that can also be used for mutual exclusion. This includes binary semaphores, which serve as a simple lock, or counting semaphores, which manages access to multiple resources.
  • Atomic operations: Hardware-level instructions enabling atomic updates.

Unit 3 - Deadlocks

• Deadlock: A situation where two or more processes are blocked indefinitely, each waiting for a resource held by another. Circular wait is a characteristic of deadlocks
• Conditions for deadlock:
  • Mutual Exclusion: Resources are non-sharable.
  • Hold and Wait: Processes can hold resources and request new resources while waiting.
  • No Preemption: Resources cannot be forcibly taken away from a process.
  • Circular Wait: A cycle of processes waiting for resources held by each other.
• Preventing Deadlocks:
  • Mutual Exclusion Avoidance (less common): Resources can be shareable instead of exclusive.
  • Hold and Wait Avoidance: Processes request all needed resources at once.
  • No Preemption: Preempt resources when deadlock is detected.
  • Circular Wait Avoidance: Resources are assigned a fixed order and processes can only request resources in that order.
• Deadlock Detection: Identifying potential deadlocks using graphs (Resource Allocation Graph).
• Deadlock Recovery: Recovering from deadlock by terminating or preempting processes.

Unit 4 - File Systems

• Introduction: A file system is a method used by an operating systems (OS) to manage and organize files and directories on storage devices.
• Components:
  • Files: Individual pieces of data (documents, programs, etc.).
  • Directories: Containers for organizing files.
  • File operations: Basic operations to manage data (create, read, write, delete, etc).
• Organization Techniques:
  • Sequential: Files stored consecutively.
  • Indexed sequential: Combines sequential and indexed access methods
  • Direct/random: Direct access to specified blocks/records
  • Hashed: Use hash functions to locate data.
  • Clustered/contiguous: Files stored in continuous blocks.

Unit 4 - Disk Scheduling Strategies

• Overview: Disk scheduling algorithms determine the order of requests to optimize disk access time.
• Common disk-scheduling algorithms:
  • First-Come, First-Served (FCFS)
  • Shortest Seek Time First (SSTF)
  • SCAN (Elevator Algorithm)
  • C-SCAN (Circular SCAN)
  • LOOK and C-LOOK
• Techniques for Rotational Optimization:
  • Track Skewing
  • Zone Bit Recording (ZBR)

Unit 4 Other Concepts

• File Allocation Table (FAT): A table that maps file blocks to their locations on the disk.
• File Access Control: Determining access rights for users/processes to files (such as read, write, or execute).
• Free space management: Managing available space on storage devices for efficient file allocation (like Bit Vector, Linked List, Grouping).

Unit 5 - Memory Organization

• Memory Hierarchy: A structure of different levels of memory (e.g., registers, cache, main memory, secondary storage) differing in speed, capacity, and cost, creating a hierarchy that balances performance and cost.
• Memory Management Strategies:
  • Contiguous: Each process is loaded into a single continuous block of memory.
  • Partitioned: Dividing memory into fixed or variable-sized partitions to accommodate different processes.
  • Paging: Dividing both physical and virtual memory into fixed-size pages; the OS uses a page table to map virtual to physical memory.
  • Segmentation: Dividing memory into logical segments based on the program's structure.
  • Virtual Memory: Using disk space to extend physical memory, loading parts of programs into memory when needed (demand paging).
• Swapping: Moving processes between physical memory and secondary storage to improve memory utilization but can cause performance bottlenecks.
• Paging (with virtual memory): This technique divides both physical and virtual memory into fixed-size blocks called pages. This allows programs to use more memory than is physically available.
• Demand Paging: Loads page parts into memory only when they are accessed (on demand).
• Thrashing: Excessively swapping pages between memory and disk, significantly degrading system performance

Dive into the foundational concepts of Operating Systems in this Unit 1 quiz. Explore key functions such as resource management, process management, and memory management that enable software to effectively interact with hardware. Understand the crucial roles an OS plays in multitasking, security, and user interface management.