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BCS401AKTU · Sem 4

Operating System

AKTU 2023-24 scheme (B.Tech 2nd Year, AICTE model curriculum) · 100 marks: 70 end-sem theory (3 hrs; Section A: 7 short questions x 2 = 14; Section B: any 3 of 5 x 7 = 21; Section C: 5 questions, one per unit, attempt 1 of 2 parts each, x 7 = 35) + 30 internal (CT 20 + TA 10). 4 credits (3-1-0). Lab BCS451 Operating System Lab (0-0-2, 1 credit) is marked separately out of 100.

Official syllabus

Revised 0 of 109 high-repeat questions

One-Night Pass Pack

Monolithic: the whole OS (file system, scheduler, drivers) runs as one large program in kernel mode; fast but hard to maintain (early UNIX, MS-DOS, Linux). Layered: OS split into layers 0 (hardware) to N (user interface); each layer uses only the layer below, so it is easy to debug but slower. Microkernel: only basic services (IPC, scheduling, low level memory) stay in the kernel; the rest run as user-space servers using message passing (Mach, QNX). Microkernel is more reliable and secure; monolithic is faster because there is less message passing.
Full-marks tip: Draw three block diagrams (one big kernel box, stacked layers, small kernel with servers around it) and finish with a comparison table on speed, reliability, size and example. Do not forget to give one real OS example for each.

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Unit-wise syllabus

U1Introduction

Weightage: Not officially published (Section C has one 7-mark question per unit; Sections A and B are not split equally)

Operating system functions and classification: batch, interactive, time sharing, real timeMultiprocessor, multiuser, multiprocess and multithreaded systemsOperating system structure, layered design, system components and servicesReentrant kernels, monolithic and microkernel systems

U2Concurrent Processes

Weightage: Not officially published (Section C has one 7-mark question per unit; Sections A and B are not split equally)

Process concept and principle of concurrencyProducer/consumer problem, mutual exclusion and the critical section problemDekker's solution, Peterson's solution, semaphores, test and setClassical problems: dining philosophers, sleeping barberInter process communication models and schemes, process generation

U3CPU Scheduling and Deadlock

Weightage: Not officially published (Section C has one 7-mark question per unit; Sections A and B are not split equally)

Scheduling concepts, performance criteria, schedulersProcess states and transition diagram, process control block, process address spaceThreads and their managementScheduling algorithms (FCFS, SJF, SRTF, priority, round robin, multilevel queue) and multiprocessor schedulingDeadlock: system model, characterization, prevention, avoidance (Banker's algorithm), detection and recovery

U4Memory Management

Weightage: Not officially published (Section C has one 7-mark question per unit; Sections A and B are not split equally)

Bare machine, resident monitorMultiprogramming with fixed and variable partitions, protection schemesPaging, segmentation, paged segmentationVirtual memory, demand paging and its performancePage replacement algorithms (FIFO, LRU, optimal), thrashingCache memory organization, locality of reference

U5I/O Management, Disk Scheduling and File System

Weightage: Not officially published (Section C has one 7-mark question per unit; Sections A and B are not split equally)

I/O devices, I/O subsystems, I/O bufferingDisk storage and disk scheduling (FCFS, SSTF, SCAN, C-SCAN, LOOK)RAID levelsFile concept, organization and access mechanisms, directories, file sharingFile system implementation issues, file protection and security

Curated video lectures

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

Operating System complete playlist (all units)

Gate Smashers · Playlist · 92 videos · Hindi

Operating System complete playlist (all units)

KnowledgeGATE by Sanchit Sir · Playlist · 82 videos · Hindi

System calls and their types

Gate Smashers · Video · Hindi · Unit 1

Producer-consumer problem using semaphores

Gate Smashers · Video · Hindi · Unit 2

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

Silberschatz, Galvin and Gagne, Operating System Concepts, Wiley (first text in the AKTU BCS401 list; Dhamdhere, Stallings and Deitel are also listed)

Exam guide students buy

Quantum Series: Operating System (BCS401) by Quantum Publications

Unit-wise short and long answers with solved AKTU papers. Buy the edition that matches your scheme code (BCS/BAS, not the old KCS/KAS).

Local market tip

Buy the Quantum printed for code BCS401 (2023-24 scheme onward), not the older KCS401 edition, from bookshops near your college around April before the even-semester exams; stock sells out, so check early.

Lab Viva Survival

BCS451: CPU scheduling programs (FCFS, SJF, priority, multilevel queue)

Q. What is the difference between turnaround time and waiting time?: → Turnaround time = completion - arrival. Waiting time = turnaround - burst, the time spent in the ready queue.
Q. Which algorithm gives the minimum average waiting time?: → SJF (or SRTF when preemptive) is optimal for average waiting time, but burst times must be known.
Q. What is the convoy effect?: → In FCFS, short processes wait behind one long CPU-bound process, which lowers CPU and device use.
Q. What is starvation and how is it fixed in priority scheduling?: → A low priority process may never run. Aging slowly raises the priority of processes that wait long.

BCS451: Banker's algorithm and resource allocation graph

Q. What is a safe state?: → A state where some order (safe sequence) exists in which every process can get its maximum need and finish.
Q. Which matrices does Banker's algorithm use?: → Available, Max, Allocation and Need, where Need = Max - Allocation.
Q. How is a wait-for graph made from a RAG?: → Remove the resource nodes and draw Pi to Pj if Pi waits for a resource held by Pj; a cycle means deadlock.

BCS451: Bounded buffer (producer-consumer) and readers-writers using semaphores

Q. What are the initial values of the semaphores in bounded buffer?: → mutex = 1, empty = buffer size n, full = 0.
Q. What is the difference between a binary and a counting semaphore?: → A binary semaphore takes only 0 or 1 (like a mutex lock); a counting semaphore can take any non-negative value to count resources.
Q. What problem does the first readers-writers solution have?: → Writers may starve because readers keep entering while at least one reader is inside.