Operating System Study Guide

This directory contains organized notes on Operating System concepts, following a logical learning progression.

Learning Path

Study these notes in order for the best learning experience:

1. Fundamentals

Topics: OS definition, architecture, protection modes, system calls, OS services

• What is an operating system?
• OS design principles
• User/kernel mode transitions
• Monolithic vs. Modular vs. Microkernel architectures
• Linux and Mac OS architecture

2. Processes and Threads

Topics: Process lifecycle, PCB, context switching, threading models

• Process vs. application
• Memory layout (code, data, heap, stack)
• Virtual addresses and address space
• Process Control Block (PCB)
• Process states and lifecycle
• Thread creation and management
• Multithreading patterns (Boss/Workers, Pipeline, Layered)

3. Synchronization

Topics: Mutexes, condition variables, deadlocks, synchronization primitives

• Data races and synchronization problems
• Mutexes and critical sections
• Condition variables
• Readers/Writers problem
• Deadlock prevention
• Spurious wake-ups
• Pthread synchronization

4. CPU Scheduling

Topics: Scheduling algorithms, fairness, real-time scheduling

• Scheduling metrics (throughput, wait time, utilization)
• FCFS, SJF, Round Robin
• Priority scheduling and priority inversion
• MLFQ (Multilevel Feedback Queue)
• Linux O(1) Scheduler
• Linux CFS (Completely Fair Scheduler)
• Multiprocessor scheduling
• Cache affinity and load balancing
• NUMA awareness

5. Memory Management

Topics: Virtual memory, paging, segmentation, page tables

• Paging and segmentation
• MMU (Memory Management Unit)
• TLB (Translation Lookaside Buffer)
• Page tables (single-level, multi-level, inverted)
• Page faults and swapping
• Memory allocators (Buddy, Slab)

6. Inter-Process Communication

Topics: IPC mechanisms, shared memory, message passing

• Message-based IPC (pipes, message queues, sockets)
• Memory-based IPC (shared memory)
• SysV vs. POSIX shared memory
• Synchronization for shared memory
• RPC (Remote Procedure Call)

7. I/O and Filesystems

Topics: Device drivers, disk I/O, filesystem structure

• I/O devices and device drivers
• CPU-device communication (MMIO, polling, interrupts)
• PIO vs. DMA
• Synchronous vs. asynchronous I/O
• Block device stack
• Virtual File System (VFS)
• Filesystem structure (ext2, inodes)
• Disk access optimizations
• Journaling

Quick Reference

Key Concepts by Topic

Process Management: PCB, context switching, fork, exec Thread Management: pthread, mutex, condition variables Scheduling: timeslice, priority, fairness, vruntime Memory: virtual address, page table, TLB, page fault IPC: shared memory, message passing, sockets I/O: device driver, interrupt, DMA, VFS

Common Patterns

• Convoy Effect: Long jobs blocking short jobs in FCFS
• Priority Inversion: Low-priority task blocking high-priority task
• Deadlock: Circular wait on resources
• Cache Affinity: Keep tasks on same CPU for cache benefits
• Readers/Writers: Multiple readers OR one writer

Study Tips

1. Start with fundamentals: Understand OS architecture and protection modes before diving into specific mechanisms
2. Follow dependencies: Processes → Threads → Synchronization → Scheduling
3. Connect concepts: Notice how scheduling relates to context switching, how IPC relates to synchronization
4. Think about trade-offs: Every design decision has pros and cons
5. Practice with examples: Work through scheduling algorithms, page table calculations, etc.

Last updated: 2026-02-01