1 OS Basics & Definition

The single most common starting topic in every computer-awareness section.

• OS is the first program loaded into memory after booting and the last to close at shutdown.
• It is also called a resource manager or master control program.
• It runs in kernel mode (privileged), while user apps run in user mode.

Common Examples (memorise the maker)

2 Functions of an Operating System

3 Components: Kernel & Shell

Types of Kernel (frequently asked)

4 Types of Operating Systems

5 Process Management & Threads

Process States

NEW  →  READY  →  RUNNING  →  TERMINATED
                ↑          │
                └──────────┘   (back to READY when time slice ends)
RUNNING → WAITING/BLOCKED (for I/O) → READY

• PCB (Process Control Block): stores all info about a process (ID, state, registers, priority).
• Context switching: CPU saves one process’s state and loads another’s.
• fork(): system call used to create a new (child) process.
• Daemon: a background process (e.g. antivirus scan, print service).

Multi- terms (very frequently confused)

6 CPU Scheduling Algorithms

Scheduling decides which process gets the CPU next. Done by the scheduler; the dispatcher actually hands over the CPU.

7 Synchronization & Deadlock

• Critical Section: code that accesses a shared resource.
• Race Condition: output depends on the timing/order of processes accessing shared data.
• Mutual Exclusion: only one process uses a resource at a time.
• Semaphore / Mutex: tools used to achieve synchronization.
• Starvation: a process waits indefinitely for the CPU/resource.

4 Necessary Conditions for Deadlock (Coffman conditions)

8 Memory Management

Memory Hierarchy (fast → slow)

Registers  →  Cache  →  RAM  →  SSD  →  Hard Disk
(fastest, smallest, costliest) ........ (slowest, largest, cheapest)

• RAM – volatile, temporary, primary memory. ROM – non-volatile, permanent (stores BIOS).
• Cache – very fast memory between CPU and RAM for frequently-used data.
• Virtual Memory – uses part of the hard disk as extra RAM (swap / page file).

Paging vs Segmentation

Key Memory Terms

Page Replacement Algorithms

FIFO     → removes the oldest loaded page (can show Belady's anomaly)
LRU      → removes the Least Recently Used page
Optimal  → removes the page not needed for the longest future time
            (lowest faults — but only theoretical)

9 File & Device Management

File System Basics

Device (I/O) Management

10 Booting (BIOS / UEFI)

Power ON → BIOS/UEFI → POST (self-test) → Bootloader → OS loaded into RAM → Ready

11 OS Security & Protection

A high-value area as exams increasingly add computer-security questions.

• Authentication — verifying identity (password, OTP, biometric, smart card).
• Authorization — deciding what an authenticated user is allowed to do.
• Access Control — file permissions Read / Write / Execute (rwx); uses ACL (Access Control List).
• Encryption — scrambling data so only authorised users can read it.
• Firewall — filters network traffic to block unauthorised access.
• User mode vs Kernel mode — protects core OS from faulty/malicious programs.
• Sandboxing — running apps in an isolated space.

Common OS-Level Threats (quick definitions)

12 Important Full Forms

13 Inventors & History Facts

14 Comparison Charts

🧠 Solved MCQs — Based on Exam Trends

Curated, high-frequency questions with answers + one-line explanations. Click “Show Answer” to self-test.

🎯 Expected / High-Probability MCQs

Newer and likely-to-appear questions on modern OS and security concepts.

📄 One-Page Quick Revision

📝 Continue Learning — Related Topics