📖Operating Systems Notes

Operating Systems (OS)

Zero-fluff engineering notes, interactive architectural diagrams, and high-yield interview frameworks for university semester exams, GATE CSE, and technical placement rounds.

10Modules

51Topics

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Module 014 Topics

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Introduction & OS Architecture

Core abstraction layers, dual-mode operations, kernel types, and system call traps.

1.1What is an OS? Definition, Abstract View & Core Goals→1.2Evolution of Operating Systems: Batch, Spooling & Multiprogramming→1.3Multitasking, Multiprocessing (SMP vs AMP) & Real-Time OS (RTOS)→1.4OS Kernel Architectures, Dual-Mode Operations & System Calls→

Module 024 Topics

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Process Management & PCB

Process memory layout, state transitions, context switching, and schedulers.

2.1Program vs Process: Active Entities & Address Space Layout→2.2Process States & 5-State / 7-State Transition Models→2.3Process Control Block (PCB) Internals & Context Switching Overhead→2.4Schedulers: Long-Term, Short-Term, Medium-Term Schedulers & Dispatcher→

Module 036 Topics

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CPU Scheduling Algorithms

Turnaround time, waiting time, Gantt charts, preemption, and starvation handling.

3.1Scheduling Criteria: Turnaround Time, Waiting Time, Response Time & Throughput→3.2Non-Preemptive Scheduling: First-Come, First-Served (FCFS) & Convoy Effect→3.3Shortest Job First (SJF) & Shortest Remaining Time First (SRTF)→3.4Priority Scheduling & Starvation (Aging Technique)→3.5Round Robin Scheduling & Time Quantum Trade-offs→3.6Multilevel Queue & Multilevel Feedback Queue Scheduling→

Module 047 Topics

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Process Synchronization & Concurrency

Critical section problems, Peterson's algorithm, hardware atomic locks, and semaphores.

4.1Race Conditions & The Critical Section Problem→4.2The 3 Mandatory Criteria: Mutual Exclusion, Progress & Bounded Waiting→4.3Software Solutions: Lock Variable, Strict Alternation & Peterson's Algorithm→4.4Hardware Synchronization: Test-and-Set Lock (TSL) & Swap Instructions→4.5Semaphores: Counting Semaphores, Binary Semaphores & Mutexes→4.6Classical Synchronization Problems: Producer-Consumer & Bounded Buffer→4.7Classical Synchronization Problems: Readers-Writers & Dining Philosophers→

Module 055 Topics

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Deadlocks: Detection, Prevention & Avoidance

Coffman conditions, Resource Allocation Graphs (RAG), and Banker's algorithm.

5.1Deadlock Characterization: The 4 Necessary Coffman Conditions→5.2Resource Allocation Graphs (RAG) & Cycle Detection→5.3Deadlock Prevention: Eliminating Coffman Conditions→5.4Deadlock Avoidance: Safe States & Banker's Algorithm Step-by-Step→5.5Deadlock Detection & Recovery Strategies→

Module 065 Topics

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UNIX System Calls & Fork Mechanics

The fork() tree hierarchy, memory copying, zombie/orphan processes, and execve().

6.1The fork() System Call: Duplication, Memory Copy & Return Codes→6.2Calculating Total Processes Created by n Successive fork() Calls→6.3Process Hierarchies: Tree Structures & Parent-Child Relationships→6.4Zombie Processes vs Orphan Processes & wait() Mechanics→6.5The exec() Family of System Calls: Replacing Process Memory→

Module 077 Topics

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Main Memory Management

Contiguous allocation, paging architecture, TLB access time, and multi-level tables.

7.1Contiguous Memory Allocation: Fixed vs Dynamic Partitioning→7.2Internal vs External Fragmentation→7.3Dynamic Storage Allocation Algorithms: First-Fit, Best-Fit & Worst-Fit→7.4Compaction & Paging Architecture (Pages, Frames & Page Tables)→7.5Address Translation Mechanics: Logical Address to Physical Address→7.6Translation Lookaside Buffer (TLB) & Effective Memory Access Time (EMAT)→7.7Multi-Level Paging, Inverted Page Tables & Segmentation→

Module 085 Topics

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Virtual Memory & Page Replacement

Demand paging, page fault cycles, FIFO, Belady's anomaly, LRU, and thrashing.

8.1Demand Paging & The Page Fault Handling Cycle→8.2Page Replacement Algorithms: First-In, First-Out (FIFO) & Belady's Anomaly→8.3Optimal Page Replacement (OPT / MIN)→8.4Least Recently Used (LRU) Page Replacement & Stack Algorithms→8.5Frame Allocation Policies & Thrashing (Working Set Model)→

Module 094 Topics

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Storage & Disk Scheduling

Magnetic disk anatomy, seek time calculation, FCFS, SSTF, SCAN, and LOOK.

9.1Magnetic Disk Anatomy: Platters, Tracks, Sectors, Seek Time & Rotational Latency→9.2FCFS & Shortest Seek Time First (SSTF) Disk Scheduling→9.3Elevator Algorithms: SCAN & C-SCAN Disk Scheduling→9.4Optimized Traversal: LOOK & C-LOOK Disk Scheduling→

Module 104 Topics

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File Systems & Inodes

File attributes, directory structures, contiguous/indexed allocation, and UNIX inodes.

10.1File Attributes, Operations & Access Methods (Sequential vs Direct)→10.2Directory Structures: Single-Level, Two-Level & Tree-Structured Directories→10.3File Allocation Methods: Contiguous, Linked & Indexed Allocation→10.4UNIX File System Internals: Inodes, Direct Blocks & Indirect Pointers→

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