SCAN Scheduling

Duration: 7 min

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Inside: a video lesson and guided study material.

Module outline

  1. About the course: About the Course
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  7. Unit 1 | Digital Electronics: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation
  8. Unit 2 | COA: Basics of COA, Floating Point Rep, Cache Memory Organization, Input Output Organisation, Instr Formats & Modes, Control Unit Design, Register Transfer and Microoperations, Programming the Basic Computer
  9. Unit 3 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  10. Unit 3 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  11. Unit 4 | Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  12. Unit 5 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management
  13. Unit 6 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Transaction Management, Concurrency Control
  14. Unit 7 | Computer Networks: Introduction to CN, Data Communication, 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
  15. Unit 8 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  16. Unit 9 | Object Oriented Programming: OOPS with C++
  17. Unit 10 | Web Development: HTML Basics, CSS, JavaScript-Basics, XML
  18. Unit 11 | 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
  19. Unit 12 | IoT: Emerging Tech Trends, Cloud Computing
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  24. Full Length Mock Tests — General Paper:
  25. Full Length Mock Tests — Computer Science (Paper II):
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This educational video delivers a comprehensive lecture on the SCAN disk scheduling algorithm, also known as the Elevator algorithm. The instructor begins by defining the core mechanism: the disk arm starts at one end of the disk and moves towards the other, servicing requests as it reaches each track. Upon reaching the end, the direction is reversed, and servicing continues. He uses visual aids to illustrate the arm's trajectory. He analyzes the impact of request arrival times on waiting periods, noting that requests behind the head must wait for the reversal. The session concludes with a structured breakdown of the algorithm's advantages, such as simplicity and lack of starvation, and disadvantages, including potential long waits for recently visited locations and unnecessary travel to disk ends.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The video opens with a slide titled "SCAN" displaying a paragraph explaining the algorithm's operation. The text states, "The disk arm starts at one end of the disk and moves towards the other end, servicing requests as it reaches each track." The instructor explains that at the other end, the direction is reversed, and servicing continues. He draws a large circle to represent the disk and a line to represent the arm, illustrating the back-and-forth movement. He explicitly mentions the comparison to an elevator, stating the arm behaves "just like an elevator in a building."

  2. 2:00 – 5:00 02:00-05:00

    The instructor delves into the specifics of request handling. He points to the slide text which reads, "If a request arrives in the queue just in front of the head, it will be serviced almost immediately." He contrasts this with requests behind the head, which must wait until the arm moves to the end, reverses direction, and comes back. He discusses the "uniform distribution of requests for cylinders," explaining that when the head reaches one end and reverses, "relatively few requests are immediately in front of the head since these cylinders have recently been serviced." He notes the heaviest density is at the other end.

  3. 5:00 – 7:09 05:00-07:09

    The slide changes to list "Advantages" and "Disadvantages." Under advantages, the text lists "Simple easy to understand and use," "No starvation but more wait for some random process," and "Low variance and Average response time." Under disadvantages, it lists "Long waiting time for requests for locations just visited by disk arm" and "Unnecessary move to the end of the disk, even if there is no request." The instructor uses his diagram to demonstrate the "unnecessary move," drawing a line to the edge to show travel.

The lecture systematically builds understanding of the SCAN algorithm, moving from a textual definition to a visual demonstration of the arm's movement and request density. The instructor connects the mechanical movement to performance metrics, explaining why the algorithm avoids starvation but suffers from specific latency issues. The final slide provides a concise summary of pros and cons, reinforcing the key takeaways for students regarding the trade-offs involved in using the SCAN scheduling method.

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