SCAN Scheduling

Duration: 7 min

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Inside: a video lesson and guided study material.

Module outline

  1. Communication Round: Vocabulary, Subject Verb Agreement (Verb Noun Agreement), Tenses, Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Direct and Indirect Speech, Active Passive Voice (Voice), Verbal Analogy (Word Based Analogy), Articles, Preposition, Conjunction, Sentence Construction, English Writing Ability, Communication Assessment
  2. Quantitative Aptitude: Ratio and Proportion (Ratios), Divisibility Rules, Data Interpretation, Mixture and Alligation, Permutation and Combination, Logarithm, Number System, HCF LCM, Speed Time and Distance, Percentage, Average, Powers and Exponents (Surds and Indices), Time and Work, Mensuration and Geometry, Age Problems, Pipe and Cistern, Probability, Profit and Loss, Simple Interest and Compound Interest, Algebra
  3. Analytical and Logical Reasoning: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Data Sufficiency, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Directions (Direction Test), Ranking, Order and Sequence, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Selection Decision Table (Decision Making), Logical Sequence Of Words, Puzzle Solving (Puzzles), Syllogisms, Seating Arrangements, Calendar, Clock, Blood Relations, Cubes & Dices, Venn Diagram, Analytical Reasoning (Counting Figures Reasoning)
  4. Cognizant Gaming Aptitude: Gamified / Game Based Aptitude
  5. Java (Cluster 1): Java
  6. ANSI SQL MySQL (Cluster 1,2,3): SQL
  7. HTML, CSS, JavaScript (Cluster 1,3): HTML, CSS, JavaScript
  8. Python (Cluster 2): Python for Placements by Yash Sir
  9. Cloud Fundamentals (Cluster 2): Emerging Tech Trends
  10. C# (Cluster 3): C#
  11. OOPs: Object Oriented Programming (OOPS)
  12. Technical Assessment (Coding): Coding Questions by Yash Sir, C Programming by Yash Sir, Programming in C++, Pseudo Codes
  13. Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  14. DBMS: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, ORDBMS, Database Security & Authorization, Query Processing & Optimization, Enhanced Data Models, Data Warehousing & Mining, Big Data Systems, NoSQL
  15. Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Windows OS, Linux OS, Security, Distributed Systems, Virtual Machines
  16. 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, Hardware basics, Network Security, Mobile Technology, Cloud Computing and IoT, Cyber and Info Security
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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