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Operating Systems

Processes and threads, CPU scheduling, synchronization, deadlock, memory, paging, virtual memory, file systems and disks, with a simulator for every algorithm.

• Online C compiler
• C code visualizer
• Operating Systems exercises with solutions

1. 1

   What an operating system does

   The OS manages the hardware and gives programs simple abstractions. User mode and kernel mode, system calls, interrupts, booting and the kinds of kernel.

2. 2

   Processes

   A process is a program in execution: its memory layout, its process control block, the five process states, context switches, and fork, exec and wait.

3. 3

   Threads and race conditions

   Threads share a process's memory but each has its own stack. Why that makes count++ unsafe: a race condition you can cause yourself, step by step.

4. 4

   CPU scheduling: FCFS and SJF

   How the scheduler picks the next process, the measures that judge it (turnaround, waiting and response time), first come first served, and shortest job first.

5. 5

   Round robin, SRTF and priority

   Preemptive scheduling with the timer: shortest remaining time first, priority scheduling with aging, round robin and the choice of time quantum, and multilevel queues.

6. 6

   Synchronization: locks and semaphores

   The critical-section problem and its three rules, Peterson's solution, hardware atomic instructions, mutex locks, semaphores, and the producer-consumer, readers-writers and dining-philosophers problems.

7. 7

   Deadlock

   When processes wait for each other forever: the four conditions, resource-allocation graphs, prevention, avoidance with the banker's algorithm, and detection and recovery.

8. 8

   Memory: addresses and allocation

   Logical and physical addresses, base and limit registers, fixed and variable partitions, first fit, best fit and worst fit, and internal and external fragmentation.

9. 9

   Paging

   Pages and frames, the page table, splitting an address into page number and offset, the TLB and effective access time, and multi-level page tables.

10. 10

    Virtual memory and page replacement

    Demand paging and what happens on a page fault, its cost, the FIFO, Optimal and LRU replacement algorithms, Belady's anomaly, and thrashing.

11. 11

    File systems

    Files and directories, contiguous, linked (FAT) and indexed allocation, inodes and the biggest file they allow, free-space bitmaps, journaling and permissions.

12. 12

    Disks and disk scheduling

    How a hard disk finds data (seek, rotation, transfer), the FCFS, SSTF, SCAN, C-SCAN, LOOK and C-LOOK algorithms, what changes with SSDs, and RAID.