Disk Basics

Duration: 32 min

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Inside: a video lesson and guided study material.

Module outline

  1. Paper - 1 | Unit - 1 | Teaching Aptitude: Concept and Objectives of Teaching / शिक्षण की अवधारणा एवं उद्देश्य, Levels of Teaching / शिक्षण के स्तर, Learner's Characteristics / शिक्षार्थी की विशेषताएँ, Learning: Nature and Theories / अधिगम: प्रकृति एवं सिद्धांत, Cognition, Memory and Metacognition / संज्ञान, स्मृति एवं अधिसंज्ञान, Factors Affecting Teaching / शिक्षण को प्रभावित करने वाले कारक, Effective Teaching and the Teacher / प्रभावी शिक्षण एवं शिक्षक, Instructional Objectives and Lesson Planning / अनुदेशनात्मक उद्देश्य एवं पाठ नियोजन, Methods of Teaching / शिक्षण विधियाँ, Offline and Online Teaching Methods / ऑफ़लाइन एवं ऑनलाइन शिक्षण विधियाँ, Teaching Support System / शिक्षण सहायक प्रणाली, Evaluation Systems / मूल्यांकन प्रणाली, Biological Basis of Emotion / संवेग का जैविक आधार, Central and Peripheral Nervous Systems / केन्द्रीय और परिधीय तंत्रिका तंत्र
  2. Paper - 1 | Unit - 2 | Research Aptitude: Research: Meaning, Features and Scientific Method / अनुसंधान: अर्थ, लक्षण व वैज्ञानिक विधि, Research Paradigms and Approaches / अनुसंधान के प्रतिमान एवं उपागम, Types of Research / अनुसंधान के प्रकार, Variables and Measurement / चर एवं मापन, Methods of Research / अनुसंधान की विधियाँ, Steps of Research / अनुसंधान के चरण, Sampling / प्रतिचयन, Tools and Methods of Data Collection / आँकड़ा संग्रह के उपकरण एवं विधियाँ, Data Analysis and Statistics in Research / आँकड़ा विश्लेषण एवं शोध सांख्यिकी, Thesis and Article Writing / शोध-प्रबंध एवं लेख लेखन, Application of ICT in Research / अनुसंधान में ICT का अनुप्रयोग, Research Ethics / शोध नैतिकता
  3. Paper - 1 | Unit - 3 | Comprehension: Literal Comprehension, Vocabulary and Language in Context, Inferential Comprehension, Critical Comprehension, Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions)
  4. Paper - 1 | Unit - 4 | Communication: Communication: Meaning, Nature and Process / संचार: अर्थ, प्रकृति एवं प्रक्रिया, Types and Levels of Communication / संचार के प्रकार एवं स्तर, Verbal and Non-verbal Communication / मौखिक एवं अमौखिक संचार, Semiotics and Meaning / संकेत विज्ञान एवं अर्थ, Models and Theories of Communication / संचार के मॉडल एवं सिद्धांत, Effective Communication / प्रभावी संचार, Barriers to Communication / संचार की बाधाएँ, Classroom Communication / कक्षा संचार, Mass Media: Types and Evolution / जनसंचार माध्यम: प्रकार एवं विकास, Mass Media and Society / जनसंचार एवं समाज, Digital and New Media / डिजिटल एवं नव माध्यम, General Awareness (Legacy Paper 1) / सामान्य जागरूकता (पुराना पेपर 1)
  5. Paper - 1 | Unit - 5 | Mathematical Reasoning and Aptitude: Number System and Simplification / संख्या पद्धति एवं सरलीकरण, Algebra and Ages / बीजगणित एवं आयु, Percentage / प्रतिशतता, Ratio, Proportion, Partnership and Mixtures / अनुपात, समानुपात, साझेदारी एवं मिश्रण, Averages / औसत, Profit, Loss and Discount / लाभ, हानि एवं बट्टा, Simple and Compound Interest / साधारण एवं चक्रवृद्धि ब्याज, Time and Work / समय एवं कार्य, Speed, Time and Distance / चाल, समय एवं दूरी, Mensuration and Geometry / क्षेत्रमिति एवं ज्यामिति, Series / श्रेणी, Coding-Decoding / कूटलेखन-कूटवाचन, Relationships, Directions and Ranking / संबंध, दिशा एवं क्रम, Arrangements, Puzzles, Clock and Calendar / व्यवस्था, पहेलियाँ, घड़ी एवं कैलेंडर, Mathematical Foundations, जीवनी, Philosophy of the Constitution / संविधान का दर्शन, Analysis, Indian Polity and Governance (Legacy Unit 10) / भारतीय राजव्यवस्था और शासन (पुराना यूनिट 10)
  6. Paper - 1 | Unit - 6 | Logical Reasoning: Structure of Arguments / युक्ति की संरचना, Terms, Definitions and Uses of Language / पद, परिभाषा एवं भाषा के उपयोग, Categorical Propositions / निरुपाधिक प्रतिज्ञप्तियाँ, Categorical Syllogism / निरुपाधिक न्यायवाक्य, Venn Diagrams / वेन आरेख, Deduction, Induction and Analogy / निगमन, आगमन एवं सादृश्यता, Fallacies / तर्कदोष, Indian Logic: Pramanas / भारतीय तर्कशास्त्र: प्रमाण, Anumana and Vyapti / अनुमान एवं व्याप्ति, Hetvabhasa / हेत्वाभास, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Aristotle / अरस्तू, Western Schools of Philosophy / पाश्चात्य दर्शन की विचारधाराएँ, Kant / कांट, Sadhana Paada, Vaiśeṣika / वैशेषिक
  7. Paper - 1 | Unit - 7 | Data Interpretation: Data and Graphical Representation / आँकड़े एवं आलेखीय निरूपण, Data Interpretation: Tables / आँकड़ा निर्वचन: तालिका
  8. Paper - 1 | Unit - 8 | Information and Communication Technology: Computer Fundamentals and Hardware, Memory, Storage and Data Representation, Computer Software, Office Applications, Multimedia and File Formats, Computer Networks, Internet and World Wide Web, Email and Online Communication, Cyber Security, Digital Ethics, IPR and Society, Cloud and Distributed Computing, Emerging Technologies, ICT in Education and Governance, Cyber Threats and Malware Attacks, Role of Internet and Web Services, Electronic Data Interchange and E-Commerce, Internet Fundamentals, Web Design & Development, Web Publishing & Hosting, Emerging Technologies, Terms & Abbreviations, Society, Law & Ethics, Keyboard Shortcuts, Website, Browser & Services, Protection of Geographical Indications / भौगोलिक संकेतों का संरक्षण
  9. Paper - 1 | Unit - 9 | People Development and Environment: Ecosystems and Biodiversity / पारितंत्र और जैव विविधता, Human and Environment Interaction / मानव और पर्यावरण की अंतःक्रिया, Development and Environment / विकास और पर्यावरण, Natural Resources – Forests, Water and Soil / प्राकृतिक संसाधन: वन, जल और मृदा, Energy Resources / ऊर्जा संसाधन, Air Pollution / वायु प्रदूषण, Water Pollution and Treatment / जल प्रदूषण और उपचार, Noise Pollution / ध्वनि प्रदूषण, Waste Management / अपशिष्ट प्रबंधन, Environmental Health and Toxicology / पर्यावरणीय स्वास्थ्य और विषविज्ञान, Climate Change and Global Environmental Issues / जलवायु परिवर्तन और वैश्विक पर्यावरणीय समस्याएँ, Natural Hazards and Disaster Management / प्राकृतिक प्रकोप और आपदा प्रबंधन, Indian Environmental Laws and Policies / भारतीय पर्यावरण कानून और नीतियाँ, International Environmental Agreements / अंतर्राष्ट्रीय पर्यावरण समझौते, Environment / पर्यावरण, Geography / भूगोल, Factory and Industry Systems / कारखाना और उद्योग व्यवस्थाएँ, Earth Materials, Surface Features and Processes, Communicable Diseases and Immunization / संक्रामक रोग और प्रतिरक्षण
  10. Paper - 1 | Unit - 10 | Higher Education System: Education in Ancient India / प्राचीन भारत में शिक्षा, Ancient Centres of Higher Learning / प्राचीन भारत के उच्च शिक्षा केंद्र, Colonial Education Policies and Commissions / औपनिवेशिक काल की शिक्षा नीतियाँ और आयोग, Colonial Colleges, Universities and Reformers / औपनिवेशिक कॉलेज, विश्वविद्यालय व सुधारक, Education Commissions and Policies after Independence / स्वतंत्र भारत में शिक्षा आयोग और नीतियाँ, National Education Policy 2020 / राष्ट्रीय शिक्षा नीति 2020, Types of Higher Education Institutions / उच्च शिक्षा संस्थानों के प्रकार, Learning Programmes and Academic Credits / अधिगम कार्यक्रम और अकादमिक क्रेडिट, Professional, Technical and Skill-Based Education / व्यावसायिक, तकनीकी और कौशल आधारित शिक्षा, Value Education and Environmental Education / मूल्य शिक्षा और पर्यावरण शिक्षा, Governance, Administration and Financing / शासन, प्रशासन और वित्तपोषण, Regulation, Accreditation and Ranking / उच्च शिक्षा का नियमन, प्रत्यायन और रैंकिंग
  11. Paper 2 | Unit 1 | Discrete Structures and Optimization: Propositional and Predicate Logic, Set Theory, Relations, Functions, Permutation, Combination and Probability / क्रमचय, संचय एवं प्रायिकता, Graph Theory, Group Theory, Digital Systems & Boolean Basics, Boolean Expression, Boolean Minimization, Optimization, Markov Chains
  12. Paper 2 | Unit 2 | Computer System Architecture: Logic Gates & Hardware, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Floating Point Rep, Basics of COA, Register Transfer and Microoperations, Programming the Basic Computer, Instr Formats & Modes, Control Unit Design, Pipelining, Input Output Organisation, Cache Memory Organization, Multiprocessors
  13. Paper 2 | Unit 3 | Programming Languages and Computer Graphics: Language Design, C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, HTML Basics, XML, JavaScript-Basics, Java, Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing, OOPS with C++, Java Fundamentals, Array, String, IO & References, OOPS with Java
  14. Paper 2 | Unit 4 | 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, Database Recovery, ORDBMS, Database Security & Authorization, Query Processing & Optimization, Enhanced Data Models, Data Warehousing & Mining, Big Data Systems, NoSQL
  15. Paper 2 | Unit 5 | System Software and Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Windows OS, Linux OS, Security, Distributed Systems, Virtual Machines
  16. Paper 2 | Unit 6 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  17. Paper 2 | Unit 7 | Data Structures and Algorithms: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  18. Paper 2 | Unit 8 | Theory of Computation and Compilers: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Complexity Theory, 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
  19. Paper 2 | Unit 9 | Data Communication and 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, Cloud Computing, Mobile Computing
  20. Paper 2 | Unit 10 | Artificial Intelligence: Approaches to AI, Search Algorithms, Game Playing, Knowledge Representation, Planning, Multi Agent Systems, Fuzzy Sets, Natural Language Processing, Artificial Neural Networks, Genetic Algorithms
  21. Full Notes: Paper 1 Full Notes
  22. Paper 1 | Full Mock Tests:
  23. Paper 2 | Full Mock Tests:
  24. Paper 1 | Previous Year Papers:
  25. Paper 2 | Previous Year Papers:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture introduces disk storage fundamentals, progressing from general secondary and optical storage to the internal mechanics of magnetic hard disk drives (HDDs) and finally to quantitative access-time calculations. The instructor begins by defining secondary storage as non-volatile, permanent, and high-capacity, contrasting it with RAM. Examples include HDDs, SSDs, magnetic tape, and optical media such as CDs, DVDs, and Blu-ray discs. The lesson then focuses on magnetic disks, explaining that data is stored magnetically on rotating platters and organized into tracks, sectors, and cylinders. Using a labeled HDD diagram and hand-drawn concentric-circle diagrams, the instructor maps physical components—platters, spindles, read/write heads, and actuator arms—to logical structures. A worked example with two platters shows that the number of surfaces equals 2 × 2 = 4, distinguishing upper and lower surfaces. The lecture then introduces logical blocks and Logical Block Addresses (LBA), stating that a logical block is the smallest unit of data transfer and that logical blocks are mapped to physical sectors in a defined order: track, cylinder, then next cylinder. Finally, the instructor defines disk access time as seek time plus rotational latency plus data transfer time plus controller overhead. Using a 6000 RPM disk, the rotation time is calculated as 60 / 6000 = 0.01 seconds, or 10 ms per rotation, and average rotational latency is half of that. A sample problem with seek time 8 ms, transfer time 2 ms, and overhead 1 ms is set up to compute total data access time.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The lecture opens with a 'Storage Basics' slide defining secondary storage as used to store data permanently, non-volatile so data remains when power is off, and providing large storage capacity. The instructor underlines 'permanently' and writes 'Unlike RAM' in pink ink to contrast secondary storage with primary memory. Examples shown include Hard Disk (HDD), Solid State Drive (SSD), and Magnetic Tape, alongside optical storage devices such as CD, DVD, and Blu-ray Disc. The instructor points to the optical storage section and notes that it is a direct-access device, using arrows to connect text descriptions to the corresponding device images.

  2. 2:00 – 5:00 02:00-05:00

    The instructor continues annotating the storage basics slide, highlighting 'non-volatile' and adding handwritten notes about SSD capacities such as 1TB, 2TB, and 3TB. Magnetic tape is circled among the secondary storage examples. The lesson then transitions to a new slide titled 'Magnetic Disk,' which states that magnetic disks provide a large part of secondary storage, that the Hard Disk Drive (HDD) is the most common magnetic disk, and that data is stored magnetically on rotating platters. A labeled HDD diagram appears showing the Platter, Spindle, Read/Write Head, and Actuator Arm, with a magnified inset of concentric rings labeled Track and Sector and a stacked-platter graphic tagged Cylinder.

  3. 5:00 – 10:00 05:00-10:00

    The instructor points to the exploded HDD diagram and underlines key phrases in pink, including 'magnetic disk' on the second bullet. The magnified inset shows concentric rings labeled Track and Sector beside a platter stack labeled Cylinder, with pink handwritten notes. To clarify disk organization, the instructor draws a pink concentric-circle diagram on the board and adds an arrow labeled 'Track.' This visual bridge connects the physical platter layout to the logical arrangement of data, emphasizing that tracks are concentric rings on a disk surface and sectors divide each track into smaller units.

  4. 10:00 – 15:00 10:00-15:00

    At the interactive whiteboard, the instructor draws a pink target-like diagram labeled 'Tracks' and 'Sector.' He writes 'No of Platters = 2' and calculates 'No of Surfaces = 2 x 2 = 4,' then sketches two pairs of concentric circles bracketed as 'Platter 0' and 'Platter 1,' labeling each pair with Upper Surface and Lower Surface. The slide states that a disk is organized into Tracks, Sectors, and Cylinders, and notes that an HDD contains moving parts such as platters and read/write heads. The cylinder concept is reinforced visually as a stack of corresponding tracks across multiple platters.

  5. 15:00 – 20:00 15:00-20:00

    The lecture moves to a slide titled 'Logical Blocks and LBA,' which states that a logical block is the smallest unit of data transfer. A 'Magnetic Disk Structure' diagram labels Track, Read/Write Head, and Actuator Arm. A Block-to-LBA table maps Block 0 through Block 5 to LBA 0 through LBA 5, and a 'Mapping Order' column shows Track, Cylinder, then Next Cylinder. A right-hand 'Key Points' panel lists numbered points including that logical blocks are mapped to the physical sectors of the disk. The instructor then turns to the whiteboard and draws concentric circles in pink marker, repeating the pattern as two sets labeled 'Upper Side' and 'Lower Side,' joined by a bracket marked 'Platters.'

  6. 20:00 – 25:00 20:00-25:00

    The instructor explains the mapping of logical blocks to physical sectors on the whiteboard, using the 'Logical Blocks and LBA' slide with its magnetic disk structure diagram and mapping order. He then introduces 'Disk Access Time,' defining seek time and rotational latency as the main components of access delay. On the whiteboard he writes formulas: '1 Rotation Time = 60 / RPM seconds' and 'Average Rotational Latency = 1/2 x Rotation Time.' A hand-drawn disk rotation diagram illustrates how the read/write head must wait for the desired sector to rotate into position, making average latency half of one full rotation.

  7. 25:00 – 30:00 25:00-30:00

    The instructor applies the access-time formulas to a concrete example. A slide shows circled terms 'Seek Time' and 'Rotational Latency,' a hand-drawn concentric disk diagram, and the note 'Rotational Speed = 6000 RPM.' A question slide states that a disk has a rotational speed of 6000 RPM, with seek time 8 ms, transfer time 2 ms, and controller overhead 1 ms. In pink marker the instructor computes '1 Sec = 6000/60 = 100' rotations per second and a round time of '10ms,' establishing the rotation period needed to find average rotational latency.

  8. 30:00 – 32:26 30:00-32:26

    The final segment consolidates the access-time calculation. The slide presents the formula 'Data Access Time = Seek Time + Rotational Latency + Data Transfer + Overhead.' Using the 6000 RPM disk, one rotation takes 10 ms, so average rotational latency is 5 ms. The instructor combines the given values—seek time 8 ms, average rotational latency 5 ms, transfer time 2 ms, and overhead 1 ms—to compute total data access time. This worked example ties together the physical disk structure, logical block mapping, and timing formulas introduced earlier in the lecture.

The lecture builds a coherent model of disk storage from abstract to quantitative. It starts by situating secondary storage within the memory hierarchy: non-volatile, permanent, and high-capacity, with HDDs, SSDs, tape, and optical media as examples. The focus then narrows to magnetic disks, where the physical components (platters, spindle, read/write head, actuator arm) are mapped to logical structures (tracks, sectors, cylinders). The two-platter example clarifies that each platter has an upper and lower surface, giving four surfaces total. Logical blocks and LBA provide the software-visible abstraction: a logical block is the smallest transfer unit, mapped to physical sectors in track-cylinder-next cylinder order. The quantitative portion defines disk access time as seek time plus rotational latency plus transfer time plus overhead, with rotation time equal to 60/RPM seconds and average rotational latency half of that. The 6000 RPM example yields a 10 ms rotation and 5 ms average latency, which is then added to the given seek, transfer, and overhead values. For exam revision, students should remember the definitions of non-volatile secondary storage, the track-sector-cylinder hierarchy, the LBA mapping order, and the access-time formula with its RPM-based latency calculation.

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