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Operating Systems

Operating Systems is one of the highest-weighted GATE CS subjects. These lessons explain each topic with figures and worked examples, use small simulators to show exactly how scheduling, paging and disk algorithms behave, and end with GATE-style questions whose numerical answers are recomputed by a program.

Start the first lesson

1Basics

  1. Introduction to Operating SystemsWhat an operating system does, user and kernel mode, system calls, interrupts and kernel designs.

2Process Management

  1. Processes and ThreadsThe process abstraction, process states, the PCB, context switches, fork(), and threads.
  2. CPU SchedulingFCFS, SJF, SRTF, priority and Round Robin scheduling, with Gantt charts and waiting-time calculations.

3Synchronization

  1. Process SynchronizationRace conditions, the critical-section problem, Peterson's solution, hardware locks and semaphores.
  2. Classic Synchronization ProblemsProducer-consumer, readers-writers and dining philosophers solved with semaphores.
  3. DeadlocksThe four necessary conditions, resource-allocation graphs, prevention, avoidance with the Banker's algorithm, and detection.

4Memory Management

  1. Memory Management BasicsLogical vs physical addresses, contiguous allocation, first/best/worst fit, and fragmentation.
  2. Paging, TLBs and Page TablesSplitting addresses into page number and offset, effective access time with a TLB, page table sizes and multilevel paging.
  3. Virtual Memory and Page ReplacementDemand paging, page faults, FIFO, LRU and Optimal replacement, Belady's anomaly and thrashing.

5Storage

  1. File SystemsFiles and directories, contiguous, linked and indexed allocation, inodes and maximum file size, free-space management.
  2. Disk Structure and Disk SchedulingSeek time, rotational latency, and the FCFS, SSTF, SCAN, C-SCAN, LOOK and C-LOOK algorithms.

6GATE Practice

  1. OS GATE Practice SetMixed GATE-style questions on processes, scheduling, synchronization, deadlocks, memory, file systems and disks.