FCFS Advantage Vs Disadvantage

Duration: 10 min

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Module outline

  1. General Intelligence & Reasoning: Analogy, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Blood Relations, Directions (Direction Test), Ranking, Order and Sequence, Logical Sequence Of Words, Syllogisms, Venn Diagram, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Selection Decision Table (Decision Making), Data Sufficiency, Puzzle Solving (Puzzles), Data Arrangement, Cubes & Dices, Calendar, Clock, Arithmetic, Number System, HCF LCM, Verbal Analogy (Word Based Analogy), Visual Recognition and Figure Completion, Paper Folding and Cutting, Transformation of Shapes, Clocks and Calendars, Direction Sense, Cubes and Dice, Patterns in Two-Dimensional Figures, Seating Arrangements, Analogy and Classification, Logical Deduction and Induction, Alphabet and Word Tests, Mathematical Operations, Series Completion, Simplification and Approximation, Coding and Decoding, Numerical Reasoning, Assembling and Grouping of Shapes, Three-Dimensional Patterns and Visualization, Vocabulary, Number System, Averages, Mixtures and Alligation, Simple and Compound Interest, Percentages, Algebra, Speed, Time and Distance, Seating and Arrangement Puzzles, Traverse Surveying, Order, Ranking and Sequence, Constraint Puzzles, Syllogisms and Venn Diagrams, Reading Comprehension, Critical Reasoning, Permutations and Combinations, Narrative Sequencing, Project Monitoring, Resources and Safety, Profit, Loss and Discount, Ratio and Proportion, Time and Work, Mensuration, Data Interpretation, Powers, Surds and Logarithms, Sequences and Series, Articles and Determiners, Sentence Completion, Data Sufficiency, Blood Relations, Simple Interest and Compound Interest, Mixture and Alligation, Sequence and Series (Series), Speed Time and Distance, Algebra, Profit and Loss, Powers and Exponents (Surds and Indices), Permutation and Combination
  2. General Awareness: Physics, Chemistry, Biology, History, Geography, Polity, Indian Economy, Environment, Static General Knowledge, GK- Current Affairs, Artificial Intelligence, MS Office Applications, Terms & Abbreviations, Keyboard Shortcuts, Evolution of Indian Banking (Banking & Financial Awareness), Emerging Tech Trends
  3. Engineering Mathematics: Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Linear Algebra, Calculus, Probability, Statistics, Signal Space and Optimum Detection, Probability, Statistics
  4. Digital Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Floating Point Rep, Number Systems and Codes, Registers and Counters, Boolean Algebra and Logic Gates, Microprocessors and Microcontrollers, Logic Families and CMOS Logic, Microprocessors, Logic Gates and Boolean Algebra, Minimization of Boolean Functions, Timing, Hazards and Testing, Logic Families, Combinational Logic Design, Arithmetic Circuits, Waveform Generators and Timer Circuits, Semiconductor Memories and Programmable Logic Devices, Combinational Logic Circuits, Latches and Flip-Flops, Finite State Machines, Sequential Circuits and State Machines, Minimization of Boolean Functions, Arithmetic Circuits, Latches and Flip-Flops, Number Systems and Codes, Registers and Counters
  5. Computer Organisation & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Programming the Basic Computer, Register Transfer and Microoperations, Semiconductor Memories and Programmable Logic, Processor Organization and Instructions, Memory Hierarchy and Input/Output, Registers and Counters
  6. Programming & Data Structures: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, HTML Basics, OOPS with C++, Java, Object Oriented Technology
  7. Databases: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, Database Security & Authorization
  8. Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos
  9. Theory of Computation: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Complexity Theory
  10. Compiler Design: Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment
  11. Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Security, Windows OS, Distributed Systems, Unix OS, Linux OS
  12. Computer Networks: Introduction to CN, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware Basics, Data Communication, Website, Browser & Services, Web Design & Development, Network Security, Cyber Threats and Malware Attacks, Cyber Safety and Security
  13. Full Length Mock Tests:
  14. Sectional Tests:
  15. Paper 2 - Full-length Mock Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video lecture provides a comprehensive overview of the First-Come, First-Served (FCFS) CPU scheduling algorithm, focusing on its characteristics, advantages, and significant drawbacks. The session begins with a discussion on the benefits of FCFS, highlighting its simplicity and ease of implementation using a standard Queue data structure. The instructor notes its suitability for background processes where execution urgency is low. The core of the lecture involves a detailed numerical analysis using two distinct scenarios to illustrate the algorithm's performance. In the first scenario, a long process arrives before a short one, leading to a high average waiting time. The instructor meticulously calculates Turnaround Time (TAT) and Waiting Time (WT) for each process using the formulas TAT=CT-AT and WT=TAT-BT, drawing a Gantt chart to visualize the execution sequence. In the second scenario, the arrival times are swapped, resulting in a drastically lower average waiting time. This comparison serves as a practical demonstration of the "Convoy Effect," where smaller processes are forced to wait behind a larger one. The lecture concludes by formally defining the Convoy Effect and listing the disadvantages of FCFS, particularly its unsuitability for time-sharing systems where quick response times are crucial. The instructor uses visual aids like traffic convoy images to make the concept relatable.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor introduces the advantages of the FCFS algorithm. The slide titled "Advantage" is visible, listing two key points: "Easy to understand, and can easily be implemented using Queue data structure" and "Can be used for Background processes where execution is not urgent." He verbally explains that because it is simple, it is often the first algorithm taught. He emphasizes that it is good for non-urgent tasks. The "KG" logo is visible in the top right corner.

  2. 2:00 – 5:00 02:00-05:00

    The instructor presents the first numerical example. A table is shown with Process P0 (Arrival Time=0, Burst Time=100) and Process P1 (Arrival Time=1, Burst Time=2). He calculates the Completion Time (CT) for P0 as 100, leading to a Turnaround Time (TAT) of 100 and Waiting Time (WT) of 0. For P1, CT is 102, TAT is 101, and WT is 99. He calculates the Average Waiting Time as (0 + 99) / 2 = 49.5. A Gantt chart is drawn showing P0 running from time 0 to 100, followed by P1 from 100 to 102. He highlights the high waiting time for the short process P1. The formulas TAT=CT-AT and WT=TAT-BT are visible in the table headers.

  3. 5:00 – 10:00 05:00-10:00

    The second numerical example is introduced with swapped arrival times: P0 (AT=1, BT=100) and P1 (AT=0, BT=2). Since P1 arrives first, it executes first. P1 finishes at CT=2, giving TAT=2 and WT=0. P0 finishes at CT=102, giving TAT=101 and WT=1. The new Average Waiting Time is (0 + 1) / 2 = 0.5. The instructor then transitions to a slide titled "Convoy Effect," explaining that smaller processes waiting for larger ones causes high average waiting time. Images of traffic convoys are used as an analogy. A "Disadvantage" slide follows, stating FCFS is troublesome for time-sharing systems. He explains that in time-sharing, users expect quick CPU access, which FCFS fails to provide efficiently. The slide text mentions "FCFS suffers from convoy which means smaller process have to wait larger process".

  4. 10:00 – 10:26 10:00-10:26

    The instructor concludes the lesson by summarizing the comparison. He points out the stark difference between the average waiting times of 49.5 and 0.5 in the two examples. This emphasizes that FCFS performance is highly dependent on the order of arrival and can lead to poor efficiency if long processes arrive early. He reiterates that to achieve less average waiting time, smaller processes should be executed before longer ones. He gestures towards the board to emphasize the point.

The lecture effectively uses a comparative approach to teach FCFS. By presenting two scenarios with identical processes but different arrival orders, the instructor clearly demonstrates the algorithm's sensitivity to input order and its primary flaw: the Convoy Effect. This visual and numerical progression helps students understand why FCFS is often considered inefficient for interactive systems. The use of real-world analogies like traffic convoys further solidifies the concept for the audience. The detailed calculation of average waiting times in both scenarios provides concrete evidence of the algorithm's limitations.

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