CS2850 Operating Systems Detailed Revision Guide

1. Memory Management

Key Concepts (From Lecture Slides 25–32)

• Static vs. Dynamic Relocation:

  • Static Relocation: Done at load time; physical addresses are fixed. Reference: 25.MemoryManagement_Intro.pdf.
  • Dynamic Relocation: Uses base/limit registers (MMU) at runtime. Reference: 26.Address_Spaces.pdf.

• Paging & Virtual Memory:

  • Virtual Address Translation: Split into page number (for page table index) and offset. Reference: 28.Virtual_Memory.pdf.
  • Two-Level Page Tables:
    • Example: 32-bit address with 12-bit top-level index → 4096 second-level tables. Each entry covers 4KB pages. 2023 Q2c.
  • Page Replacement Algorithms: NFU, LRU, FIFO. Reference: 30.Page_Replacement_Algorithms.pdf.

Sample Questions & Strategies

• Q: “How many second-level page tables exist in a 32-bit system with 12-bit top-level index?”
  Answer: (2^{12} = 4096) tables. Each second-level table has (256) entries.

• Q: “Compare contiguous vs. linked-list file allocation.”
  Answer: Linked list avoids external fragmentation but increases access time. Ref: 35.Files_Directories_Implementation.pdf.

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2. Process Scheduling

Key Concepts (From Slides 21–24)

• Batch Systems:
  • Shortest Job First (SJF): Minimizes average waiting time. Reference: 22.Scheduling_Batch_Systems.pdf.
• Interactive Systems:
  • Round Robin (RR): Uses time slices (e.g., 20ms quantum). Reference: 23.Scheduling_Interactive_Systems.pdf.

Sample Questions & Strategies

• Q: “Compare SJF and FCFS.”
  Answer: SJF reduces average wait time but risks starvation; FCFS suffers from convoy effect. 2022 Q1b.

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3. Concurrency & Synchronization

Key Concepts (Slides 10–20, 38–41)

• Mutual Exclusion:
  • Peterson’s Algorithm: For two processes with turn and interested flags. Reference: 12.IPCBusyWaitingPeterson.pdf.
• Semaphores: Use up()/down() for synchronization (e.g., producer-consumer). Reference: 15.IPCWithoutBW_Semaphores.pdf.

Sample Questions & Strategies

• Q: “Apply Banker’s Algorithm to determine safe state.”
  Steps: Check available resources ≥ max need → grant → repeat. Reference: 40.Avoiding_Deadlocks.pdf.

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4. File Systems

Key Concepts (Slides 33–37)

• FAT vs. Linked List:
  • FAT: Centralized table for pointers → faster random access. 2022 Q3a.
• UNIX File Systems: i-nodes, Ext4 features. Reference: 45.IO_Linux.pdf.

Sample Questions

• Q: “Explain FAT allocation.”
  Answer: Avoids fragmentation with table-based block pointers. Ref: 36.Example_File_Systems.pdf.

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5. Virtualization & Security

Key Concepts (Slides 49–51)

• Hypervisors:
  • Type 1 (bare-metal, e.g., VMware ESX) vs. Type 2 (hosted). Reference: 51.Cloud_VMWare.pdf.
• Linux Security: UID/GID, file permissions. Reference: 46.Security_Linux.pdf.

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6. C Programming & OS Concepts

Key Concepts (202425_CS2850_w1_slides.pdf, 43–48)

• Dynamic Memory: malloc/free for heap allocation. Forgetting free causes leaks. 2023 Q3a.
• String Handling: Null-terminate strings to prevent overflows. Example: copyString in 2022 uses SIZE-1.

Sample Questions

• Q: “Why null-terminate before passing to merge?”
  Answer: C strings require \0 for termination. Uninitialized char c risks UB. 2023 Q3a.

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Exam Strategy

• Theory Questions: Use bullet points with slide references (e.g., “As per 28.Virtual_Memory.pdf…”).
• Coding Problems:
  • For pointers/structs: Validate assignments (e.g., p->x = 1 vs. *p.x).
  • Avoid Errors: Use sizeof(struct) and initialize variables. 2024 Q1a.

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Adapted from Lecture Topics: Processes (fork(), exec()), I/O (DMA vs. Interrupts).
Good luck! 🖥️