SJF Scheduling

Duration: 10 min

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Inside: a video lesson and guided study material.

Module outline

  1. About the Course: About the Course
  2. Section 1 | Language (Hindi): भाषा, लिपि, ध्वनि, वर्ण, अक्षर, स्वर, व्यंजन, मात्रा और संयुक्ताक्षर, वर्तनी, वर्ण-विन्यास, अनुस्वार, अनुनासिक, चंद्रबिंदु और ‘र’ के रूप, शब्द, पद और शब्द-भेद, संज्ञा और सर्वनाम, विशेषण और क्रिया, लिंग, वचन, पुरुष और कारक, काल, वाच्य, वाक्य और वाक्य-भेद, संधि, समास, विलोम शब्द, पर्यायवाची शब्द, सामान्य अशुद्धियाँ, अनेक शब्दों के लिए एक शब्द, मुहावरे और लोकोक्तियाँ, अपठित गद्यांश और अपठित पद्यांश, Multi-Topic Content (Cross-Concept Material), वर्णमाला
  3. Section 1 | Language (उर्दू भाषा — 22 प्रश्न (निश्चित)): Spelling & Diacritics, Grammar (اسم, فعل, صفت, ضمیر), Vocabulary, Idioms & Proverbs, Comprehension
  4. Section 1 | Language (বাংলা / बांग्ला भाषा — 22 प्रश्न (निश्चित)): Bangla Script and Sounds, Bangla Grammar and Usage, Bangla Word Formation and Vocabulary, Reading and Text Interpretation
  5. Section 1 | Language (English): Vocabulary, Noun, Subject Verb Agreement (Verb Noun Agreement), Adjectives, Tenses, Pronoun, Verb, Adverb, Preposition, Articles, Determiner, Conjunction, Modals, Active Passive Voice (Voice), Direct and Indirect Speech, Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Construction, Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Verbal Analogy (Word Based Analogy), Facts, Inference and Judgements
  6. Section 2 | Primary Maths & Reasoning: Ratio and Proportion (Ratios), Divisibility Rules, Mixture and Alligation, Permutation and Combination, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Percentage, Average, Profit and Loss, Simple Interest and Compound Interest, Time and Work, Mensuration and Geometry, Age Problems, Arithmetic, Powers and Exponents (Surds and Indices), Algebra, Probability, Trigonometry, Syllogisms, Seating Arrangements, Blood Relations, Directions (Direction Test), Analytical Reasoning (Counting Figures Reasoning), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Venn Diagram, Data Arrangement, Inequality, Analogy, Ranking, Order and Sequence
  7. Section 2 | General Awareness (GK + Current Affairs): Polity, Physics, Biology, State Wise GK, Chemistry, History, Geography, Indian Economy, Environment, GK- Current Affairs, Static General Knowledge
  8. Section 3 | Computer System and Org. (CSO): Basics of COA, Floating Point Rep, Cache Memory Organization, Instr Formats & Modes, Programming the Basic Computer, Input Output Organisation, Register Transfer and Microoperations, Control Unit Design
  9. Section 3 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, SQL, File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control
  10. Section 3 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Process Synchronization
  11. Section 3 | Computer Networks: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics
  12. Section 3 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Minimum Spanning Trees, Shortest Path Algos
  13. Section 3 | Theory Of Computation & Compiler Design: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization
  14. Section 3 | Emerging Trends (AI, Societal Ethics & MS Office): Artificial Intelligence, Emerging Tech Trends, Society, Law & Ethics, MS Office Applications
  15. Section 3 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Maintenance and Configuration Management, Software Testing
  16. Section 3 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  17. Section 3 | OOPS, C++, JAVA, HTML: OOPS with C++, Java, HTML Basics, CSS
  18. Section 3 | Java: Java Fundamentals, Array, String, IO & References
  19. Section 3 | Python: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  20. Section 3 | Digital Electronics: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation
  21. Section 3 | Multimedia: Multimedia
  22. BPSC Previous Year Papers:
  23. BPSC Full Mock Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video lecture provides a comprehensive overview of CPU scheduling algorithms, specifically focusing on Shortest Job First (SJF) and Shortest Remaining Time First (SRTF). The instructor begins by defining the core principle of these algorithms: selecting the process with the smallest burst time for CPU execution. He distinguishes between the non-preemptive nature of SJF and the preemptive nature of SRTF, noting that SRTF is a 'purely greedy approach.' The lecture then transitions into a detailed numerical problem involving five processes. The instructor demonstrates how to construct a Gantt chart, calculate Completion Time (CT), Turn Around Time (TAT), and Waiting Time (WT) for each process, and finally compute the average waiting time. This practical application reinforces the theoretical concepts introduced at the start of the session.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The video opens with a slide titled 'Shortest Job First (SJF)(non-pre-emptive)' and 'Shortest Remaining Time First (SRTF)/ (Shortest Next CPU Burst) (Pre-emptive)'. The instructor explains the fundamental rule: 'Whenever we make a decision of selecting the next process for CPU execution, out of all available process, CPU is assigned to the process having smallest burst time requirement.' He clarifies that if there is a tie in burst times, First Come First Serve (FCFS) is used to break the tie. He also notes that SRTF is a 'purely greedy approach' because it supports both non-preemptive and preemptive versions. The instructor emphasizes that the decision is made based on the smallest burst time requirement among available processes. The slide text explicitly states: 'When the CPU is available, it is assigned to the process that has the smallest next CPU burst.'

  2. 2:00 – 5:00 02:00-05:00

    The instructor focuses on the non-preemptive nature of SJF. He writes on the whiteboard: 'In Shortest Job First (SJF)(non-pre-emptive) once a decision is made and among the available process, the process with the smallest CPU burst is scheduled on the CPU, it cannot be pre-empted even if a new process with the smaller CPU burst requirement then the remaining CPU burst of the running process enter in the system.' He draws a small example table with processes P1, P2, and P3, listing their Arrival Time (AT) and Burst Time (BT) to illustrate the concept. He explains that once a process starts, it runs to completion regardless of new arrivals with shorter burst times. This section sets the theoretical groundwork for the numerical problem that follows. He specifically writes 'P1 0 5', 'P2 0 4', 'P3 1 1' on the board to show a scenario where P1 starts but P3 arrives later with a smaller burst.

  3. 5:00 – 9:42 05:00-09:42

    The instructor solves a numerical problem with five processes (P0 to P4). A table shows Arrival Times (1, 2, 3, 4, 5) and Burst Times (7, 5, 1, 2, 8). He draws a Gantt chart at the bottom. P0 arrives at t=1 and runs for 7 units, finishing at t=8. At t=8, P2 (BT=1) is selected as it has the smallest burst time among available processes (P1, P2, P3, P4). P2 runs from 8 to 9. Next, P3 (BT=2) is selected, running from 9 to 11. Then P1 (BT=5) runs from 11 to 16. Finally, P4 (BT=8) runs from 16 to 24. He calculates Completion Time (CT), Turn Around Time (TAT = CT - AT), and Waiting Time (WT = TAT - BT) for each process. For example, P0 has CT=8, TAT=7, WT=0. P1 has CT=16, TAT=14, WT=9. P2 has CT=9, TAT=6, WT=5. P3 has CT=11, TAT=7, WT=5. P4 has CT=24, TAT=19, WT=11. He concludes by calculating the average waiting time. The formulas are clearly written on the slide: 'Turn Around Time (TAT) = CT - AT' and 'Waiting Time (WT) = TAT - BT'.

The lecture effectively transitions from theoretical definitions to practical application. It starts by defining SJF and SRTF, highlighting the key difference in preemption. The instructor then demonstrates the non-preemptive logic with a small board example before tackling a comprehensive numerical problem. The step-by-step calculation of CT, TAT, and WT, along with the Gantt chart, provides a clear method for solving scheduling problems. This progression ensures students understand both the 'why' and the 'how' of CPU scheduling algorithms. The 'purely greedy approach' mentioned is key to understanding why SRTF minimizes waiting time.

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