SCAN Scheduling

Duration: 7 min

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Inside: a video lesson and guided study material.

Module outline

  1. About Course: UPPSC Course Overview
  2. Interview Preparation & Guidance: Interview Preparation
  3. Paper 1 | General 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, वर्णमाला, समास, संधि, 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)
  4. Paper 2 | General Studies: State Wise GK, Polity, Geography, History, GK- Current Affairs
  5. Paper 1 | Programming Language: Language Design, C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, OOPS with C++
  6. Paper 1 | Database Management Systems: 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, ORDBMS, NoSQL
  7. Paper 1 | Cyber Security: Society, Law & Ethics, Cyber Threats and Malware Attacks, Role of Internet and Web Services, Security in Mobile and Wireless Computing, Electronic Data Interchange and E-Commerce, Physical Security and Cryptography Basics, Intrusion Detection Systems (IDS), Cyber Safety and Security, Ethical Hacking
  8. Paper 1 | Computer Organization and Architecture: Basics of COA, Programming the Basic Computer, Cache Memory Organization, Input Output Organisation, Instr Formats & Modes, Register Transfer and Microoperations, Control Unit Design
  9. Paper 1 | 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
  10. Paper 1 | Design and Analysis of Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  11. Paper 1 | Data Structures: Introduction to DS, Array, Linked List, Stack, Queue, Tree, Graphs, Hashing
  12. Paper 1 | Discrete Structures and Theory of Logic: Permutation and Combination, Set Theory, Relations, Functions, Propositional and Predicate Logic, Graph Theory, Group Theory
  13. Paper 1 | Software Project Management: Software Project Management
  14. Paper 2 | Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Unix OS, Linux OS, Security
  15. Paper 2 | 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, Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Pushdown Automata & CFG, Complexity Theory
  16. Paper 2 | Artificial Intelligence & High Performance Computing: Approaches to AI, Search Algorithms, Game Playing, Knowledge Representation, Planning, Multi Agent Systems, Natural Language Processing, Emerging Tech Trends
  17. Paper 2 | Image Processing: Digital Image Fundamentals, Image Enhancement, Image Restoration, Color Image Processing, Image Compression
  18. Paper 2 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  19. Paper 2 | Computer Graphics: Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing
  20. Paper 2 | Web Technologies: Website, Browser & Services, Internet Fundamentals, Web Design & Development, Protocols & Services, Web Publishing & Hosting, Server Side & Security, Emerging Technologies, HTML Basics, JavaScript-Basics, Java
  21. Paper 2 | Soft Computing: Fuzzy Sets, Artificial Neural Networks, Genetic Algorithms
  22. Paper 2 | Distributed System: Distributed Systems
  23. UPPSC Live Class Recordings: UPPSC Polytechnic Lecturer 2025 (CS)
  24. Previous Year Papers:
  25. Mock Test:
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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