Operating Systems

Core Concepts

Core Concepts

1. Process Management

• Process vs. Program: A program is a passive set of instructions on disk. A process is a program in execution.
• Process State: The current state of a process (e.g., new, running, waiting, ready, terminated).
• CPU Scheduling: The OS must decide which process gets to use the CPU and for how long.
  • Scheduling Algorithms: First-Come, First-Served (FCFS), Shortest-Job-Next (SJN), Round Robin.
• Inter-Process Communication (IPC): Mechanisms for processes to communicate with each other (e.g., pipes, shared memory).

2. Memory Management The OS is responsible for allocating and deallocating memory space to programs that need it.

• Virtual Memory: A technique that gives a process the illusion that it has its own contiguous private memory space, which can be larger than the physical RAM.
• Paging: Dividing memory into fixed-size blocks called pages.
• Segmentation: Dividing memory into logical segments of varying sizes (e.g., code segment, data segment).
• Page Replacement Algorithms: When memory is full, the OS must decide which page to swap out (e.g., FIFO, LRU - Least Recently Used).

3. File System Management The OS provides a structured way to store and access files on storage devices.

• Files and Directories: The OS organizes data into files and folders (directories) in a hierarchical structure.
• File Operations: Creating, reading, writing, deleting files.
• Access Control: Managing permissions to determine who can read, write, or execute files.
• Common File Systems: NTFS (Windows), APFS (macOS), EXT4 (Linux).

4. Concurrency and Synchronization Managing multiple processes or threads that execute concurrently.

• Threads: The smallest unit of processing that can be performed in an OS. A process can have multiple threads.
• Race Condition: A situation where the result of an operation depends on the unpredictable sequence or timing of other events.
• Deadlock: A state in which two or more processes are blocked forever, each waiting for the other to release a resource.
• Synchronization Primitives: Tools to prevent race conditions and deadlocks.
  • Mutexes (Mutual Exclusion): Ensures that only one thread can access a critical section of code at a time.
  • Semaphores: A more general synchronization tool that can allow a certain number of threads to access a resource.

5. I/O Management The OS manages communication with hardware devices like disks, keyboards, printers, and network cards through device drivers.

Examples & Use Cases

Examples & Use Cases

Analogy for a Process Imagine cooking a recipe.

• The Program: The written recipe in a cookbook.
• The Process: You, the chef, actually gathering ingredients and following the steps.
• The CPU: The countertop space where you are actively working.
• I/O Waiting: Waiting for the oven to preheat.

Mutex in Pseudocode

// Both Thread A and Thread B want to increment a shared counter
shared_variable counter = 0;
mutex lock;

function increment_counter() {
  lock.acquire(); // Acquire the lock
  // --- Critical Section Start ---
  int temp = counter;
  temp = temp + 1;
  counter = temp;
  // --- Critical Section End ---
  lock.release(); // Release the lock
}

Without the mutex, a race condition could occur where both threads read the same value of counter and only one increment is saved.

Practice Questions

Practice Questions

1. MCQ: What is the primary purpose of virtual memory? A) To make the computer run faster. B) To allow a program to use more memory than is physically available. C) To store files permanently. D) To manage CPU scheduling.

2. Short Answer: What is a deadlock? Give a simple real-world analogy.

3. Problem: Consider three processes with the following CPU burst times: P1 (24ms), P2 (3ms), P3 (3ms). If they arrive in the order P1, P2, P3, what is the average waiting time using the First-Come, First-Served (FCFS) scheduling algorithm?

Quick Summary

Quick Summary

• The Operating System is the core software that manages a computer's hardware and software resources.
• Process Management deals with executing programs and scheduling CPU time.
• Memory Management handles the allocation of RAM and the use of virtual memory.
• File System Management provides a structured way to handle data on storage devices.
• Concurrency and Synchronization are crucial for managing multiple tasks that run at the same time, preventing issues like deadlocks and race conditions.