SJF Scheduling

Duration: 10 min

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Inside: a video lesson and guided study material.

Module outline

  1. About Course: About the Course
  2. Section A: General Awareness: Polity, Physics, Biology, Chemistry, Static General Knowledge, History, Geography, Indian Economy, GK- Current Affairs, Evolution of Indian Banking (Banking & Financial Awareness), Environment
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  8. Section B: Computer Networks, TCP/IP & Network Security: Introduction to CN, Data Communication, DLL: Flow Control, DLL: Access 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, Network Access Technologies, Network Security, Society, Law & Ethics, Mobile Computing, Net Layer:Routing Protocol, Cyber Safety and Security
  9. Section B: Teaching Methodology: Child Development, Concept of Pedagogy, Theories, Inclusive Education, Experiential Pedagogy, Assessment & Evaluation, Curriculum Framework & Reforms, National Education Policy (NEP) 2020, Psychology, Teaching-Learning Process, Personality Development, Teaching Methods & Strategies, Learning and Motivation, Learners & Learning Process, Factors Affecting Teaching, Methods of Teaching, Nature, Objectives & Characteristics of Teaching, Teaching-Learning Aids & ICT Integration, Classroom Management & Communication, Evaluation, Assessment & Measurement, Curriculum & School Environment, Inclusive Education & Special Needs, Professional Development & Ethics
  10. Section B: Digital Electronics / Boolean Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Analog-Digital Conversion
  11. Section B: Operating Systems & Linux: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, File Management, Disc Scheduling, Unix OS, Linux OS, Distributed Systems, Windows OS
  12. Section B: Data Base Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, Relational Algebra, SQL, File Organization & Indexing, Transaction Management, Concurrency Control, Database Security & Authorization, Database Recovery, Data Warehousing & Mining
  13. Section B: Internet & Web Technologies: Website, Browser & Services, Internet Fundamentals, Web Design & Development, Protocols & Services, Web Publishing & Hosting, Server Side & Security, HTML Basics, CSS, Emerging Technologies, JavaScript-Basics, .Net Programming, Electronic Data Interchange and E-Commerce, XML
  14. Section B: Computer Fundamentals, IT Basics & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Register Transfer and Microoperations, Control Unit Design, Programming the Basic Computer, Terms & Abbreviations, MS Office Applications, Instr Formats & Modes, Floating Point Rep
  15. Section B: Python Language: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  16. Section B: Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management, extras, Fundamentals of Systems and Information Systems
  17. Section B: Design & Analysis of Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  18. Section B: Mathematics: Linear Algebra, Calculus, Trigonometry, Vectors, Set Theory, Functions, Relations, Propositional and Predicate Logic, Research Process Steps, Graph Theory
  19. Section B: Computer Graphics, Multimedia & Mobile Computing: Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing, Multimedia
  20. Section B: Emerging Trends: Emerging Tech Trends, Knowledge Representation, Natural Language Processing
  21. DSSSB Previous Year Paper:
  22. Business Studies and Management: Business Communication, Business Organization and Management, Financial Accounting, Business Economics, Management Information System (MIS), Knowledge Management & New Economy
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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