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BCS303VTU · Sem 3

Operating Systems

VTU 2022 scheme (B.E. CSE and allied, from 2023-24), Integrated Professional Core Course (IPCC) · 100 marks: 50 SEE + 50 CIE, 4 credits (L:T:P 3:0:2). SEE is a 3-hour theory paper of 100 marks scaled to 50: 10 questions of 20 marks (2 per module, up to 3 sub-questions each), answer 5 full questions choosing one from each module; questions can come from the practical part too. CIE 50 = 25 theory (two internal tests plus other assessment, scaled) + 25 practical (15 for conduct, record and viva, 10 for a lab test). There is no separate practical SEE. Minimum 18/50 in SEE, 20/50 in CIE, 40/100 overall.

Official syllabus

Revised 0 of 1010 high-repeat questions

One-Night Pass Pack

An OS is a program that manages the computer hardware and acts as an intermediary between the user and the hardware (resource allocator and control program). Dual mode: a mode bit in hardware, 0 = kernel (monitor) mode, 1 = user mode. Privileged instructions (I/O, timer, interrupt control) run only in kernel mode; trying them in user mode causes a trap. A system call or interrupt switches user to kernel mode; the OS sets the bit back to user before returning. It protects the OS and other users from errant programs; a timer stops a program from holding the CPU forever.
Full-marks tip: Draw the figure: user process executing, system call (trap, mode bit = 0), kernel executes, return (mode bit = 1). Give two examples of privileged instructions. Write the definition from both user and system viewpoints.

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Unit-wise syllabus

U1Introduction to Operating Systems and System Structures

Weightage: Equal share: 1 of 5 modules (~20%), 2 questions per module in SEE

What operating systems do, computer system organization and architectureOperating system structure and operations, dual mode operationProcess, memory and storage management, protection and securityDistributed and special purpose systems, computing environmentsOperating system services, user interface, system calls and their types, system programsOS design and implementation, OS structure (layered, microkernel, modules), virtual machines, OS generation and system boot

U2Process Management, Multithreaded Programming and Process Scheduling

Weightage: Equal share: 1 of 5 modules (~20%), 2 questions per module in SEE

Process concept, process states and PCB, process scheduling, operations on processesInterprocess communication: shared memory and message passingMultithreading overview, multithreading models, thread libraries, threading issuesScheduling criteria and algorithms: FCFS, SJF, SRTF, priority, round robin, multilevel queueThread scheduling and multiple processor scheduling

U3Process Synchronization and Deadlocks

Weightage: Equal share: 1 of 5 modules (~20%), 2 questions per module in SEE

Critical section problem, Peterson's solution, synchronization hardwareSemaphores and classical problems: bounded buffer, readers-writers, dining philosophersDeadlock system model, characterization, resource allocation graphDeadlock prevention, avoidance (Banker's algorithm), detection and recovery

U4Memory Management and Virtual Memory

Weightage: Equal share: 1 of 5 modules (~20%), 2 questions per module in SEE

Address binding, swapping, contiguous allocation (first fit, best fit, worst fit)Paging, TLB, structure of the page table, segmentationDemand paging, page fault handling, copy on writePage replacement (FIFO, optimal, LRU), allocation of frames, thrashing

U5File System, Secondary Storage and Protection

Weightage: Equal share: 1 of 5 modules (~20%), 2 questions per module in SEE

File concept, access methods, directory and disk structure, file system mounting, file sharingFile system structure and implementation, directory implementationAllocation methods (contiguous, linked, indexed), free space managementMass storage structure, disk scheduling (FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK), disk managementProtection: goals, principles, domain of protection, access matrix

Curated video lectures

Free lectures from well-known educators, matched to units. Videos load only when you tap “Watch here”, to save data.

Operating Systems lectures (process, scheduling, synchronization, memory, files)

Prof. Mythili Vutukuru (IIT Bombay) · Playlist · 33 videos · English

Operating System complete playlist (all modules)

Gate Smashers · Playlist · 92 videos · Hindi

Operating System complete playlist (all modules)

KnowledgeGATE by Sanchit Sir · Playlist · 82 videos · Hindi

Introduction to operating systems

Neso Academy · Video · English · Unit 1

Producer-consumer (bounded buffer) using semaphores

Gate Smashers · Video · Hindi · Unit 3

Banker's algorithm for deadlock avoidance with example

Gate Smashers · Video · Hindi · Unit 3

LRU page replacement algorithm

Gate Smashers · Video · Hindi · Unit 4

Exam Guide Radar

Standard textbook

Abraham Silberschatz, Peter Baer Galvin and Greg Gagne, Operating System Principles, 8th Edition, Wiley India, 2015

Exam guide students buy

Sunstar Exam Scanner for VTU 3rd semester CSE (2022 scheme), or another VTU Operating Systems guide that prints code BCS303

Pick the 2022-scheme edition: question banks are arranged module-wise with solved VTU papers.

Local market tip

Check that the guide prints BCS303 and the 2022 scheme; older 21CS44 or 18CS43 books (4th semester) cover almost the same topics but follow a different module split, so buy the BCS303 edition before the first IA test.

Lab Viva Survival

BCS303 practical 1: Process system calls fork(), exec(), wait() and process termination

Q. What does fork() return?: → 0 in the child, the child's PID in the parent, and -1 if creation fails.
Q. How many processes do three fork() calls in a row create?: → 2^3 = 8 processes in total, including the original.
Q. What is a zombie process and an orphan process?: → A zombie has finished but its parent has not called wait(); an orphan's parent has exited and it is adopted by init/systemd.

BCS303 practical 2: CPU scheduling simulation (FCFS, SJF, Round Robin, Priority)

Q. What happens if the Round Robin time quantum is very large or very small?: → Very large makes it behave like FCFS; very small causes too many context switches and overhead.
Q. Which scheduling algorithms are preemptive?: → Round Robin, SRTF and preemptive priority. FCFS and non-preemptive SJF are not.

BCS303 practical 3: Producer-consumer using semaphores

Q. What are wait() and signal() on a semaphore?: → wait (P) decrements and blocks if the value is not positive; signal (V) increments and wakes a waiting process. Both are atomic.
Q. What goes wrong if wait(mutex) is done before wait(empty) in the producer?: → A producer can hold mutex while blocked on a full buffer, so the consumer can never enter: deadlock.

BCS303 practical 7: Page replacement (FIFO and LRU)

Q. What is a page fault?: → A reference to a page not in main memory; the OS traps, loads it from disk, updates the page table and restarts the instruction.
Q. What is Belady's anomaly?: → With FIFO, adding more frames can increase the number of page faults; LRU and Optimal never show it.
Q. How can LRU be implemented?: → With a counter (time stamp) per page or a stack of page numbers; the program usually keeps the last-used time of each frame.