CS2850 Operating Systems Comprehensive Revision Guide

(Based on Past Papers 2022-2024 & Lecture Slides)

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1. Exam Format Analysis

• Theory Questions (60%):

  • Definitions (e.g., kernel vs. user mode).
  • Algorithm comparisons (e.g., SJF vs. FCFS).
  • Case studies (e.g., page replacement, deadlock avoidance).

• Programming/C-Based Exercises (40%):

  • Pointer manipulation (e.g., swapping values).
  • Dynamic memory management (e.g., malloc, free).
  • String operations (e.g., merging, truncation).

Key Topics: Memory management, process scheduling, IPC, file systems, deadlocks, virtualization.

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2. Core Concepts & Guidance

Memory Management

Key Slides: 25-32, 44

Static vs. Dynamic Relocation

• Static: Addresses bound at compile time. Example: Early OS without multiprogramming.
• Dynamic: Addresses bound at runtime using base/limit registers. Example: Modern virtual memory.
• Exam Focus: Explain how dynamic relocation supports multiprogramming.

Page Replacement Algorithms

• NFU: Selects pages with the lowest usage counter.
• FIFO, LRU, Optimal: Trade-offs in overheads and efficiency.
• Example Q: Given R/M bits, justify which page is evicted by NFU.

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Process Scheduling

Key Slides: 21-24, 49

Batch Systems

• SJF: Minimizes average waiting time (requires prior burst time knowledge).
• Advantage over FCFS: Reduces starvation for short jobs.

Interactive Systems

• Round Robin: Uses time slices (quantums).
• Exam Focus: Explain how quantum size impacts throughput vs. latency.
• Example Q: Calculate turnaround time for processes with given burst times.

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Inter-Process Communication (IPC)

Key Slides: 10-20

Critical Sections

• Solutions: Peterson’s algorithm, semaphores, monitors.

Producer-Consumer Problem

• Exam Focus: Implement using sleep/wakeup primitives vs. semaphores.

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File Systems

Key Slides: 34-37

FAT vs. Linked-List Allocation

• FAT: Faster seek times via table-based block tracking.
• Example Q: Compare MS-DOS and UNIX V7 directory structures.

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Deadlocks

Key Slides: 38-41

Banker’s Algorithm

• Steps: Calculate Need = Max – Allocated, check safe sequence.
• Exam Focus: Analyze resource allocation graphs for deadlocks.

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Virtualization

Key Slides: 50-51

• Hypervisors:
  • Type 1 (bare-metal) vs. Type 2 (hosted).
  • VMware ESX: Resource isolation advantages.

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3. Programming Tasks Breakdown

Key Slides: W1 slides, 46-48

Pointer Manipulation

• Example: Swap values using swapx(int *p1, int *p2).
• Pitfall: Avoid forgetting dereferencing (*p1 vs. p1).

Dynamic Memory

• Always check malloc return values.
• Example (pure text format):
  char *s = malloc(SIZE);
if (s != NULL) {
copyString(input, s); // Ensure null-termination
free(s); // Prevent leaks
}

String Operations

• Truncation: Reserve space for \0 with i < SIZE-1.
• Exam Focus: Explain strcpy buffer overflow risks.

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4. Exam Strategy

Theory Questions

• Use structured answers: Define → Compare → Example from slides (e.g., MULTICS segmentation).

Programming Questions

• Outline logic with pseudocode first.
• Test edge cases (empty strings, maximum buffer sizes).

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5. Cheat Sheet

Key Formulas & Algorithms

• CPU Utilization: [Formula].
• Banker’s Algorithm: Ensure system stays in a safe state.

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Final Tips:

• Revise Linux system calls (clone(), fork() from slides 42-49).
• Practice past papers using frameworks above.

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End of Revision Guide – Covers all 57 files & exam trends.