Least Recently Used Page Replacement Algorithm

Duration: 6 min

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  1. About the Course: About the Course
  2. Section 1 | Language (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, संधि, समास, 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), वर्णमाला
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  5. Section 1 | Language (English): Vocabulary, Noun, Subject Verb Agreement (Verb Noun Agreement), Adjectives, Tenses, Pronoun, Verb, Adverb, Preposition, Articles, Determiner, Conjunction, Modals, Active Passive Voice (Voice), Direct and Indirect Speech, Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Construction, Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Verbal Analogy (Word Based Analogy), Facts, Inference and Judgements
  6. Section 2 | Primary Maths & Reasoning: Ratio and Proportion (Ratios), Divisibility Rules, Mixture and Alligation, Permutation and Combination, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Percentage, Average, Profit and Loss, Simple Interest and Compound Interest, Time and Work, Mensuration and Geometry, Age Problems, Arithmetic, Powers and Exponents (Surds and Indices), Algebra, Probability, Trigonometry, Syllogisms, Seating Arrangements, Blood Relations, Directions (Direction Test), Analytical Reasoning (Counting Figures Reasoning), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Venn Diagram, Data Arrangement, Inequality, Analogy, Ranking, Order and Sequence
  7. Section 2 | General Awareness (GK + Current Affairs): Polity, Physics, Biology, State Wise GK, Chemistry, History, Geography, Indian Economy, Environment, GK- Current Affairs, Static General Knowledge
  8. Section 3 | Computer System and Org. (CSO): Basics of COA, Floating Point Rep, Cache Memory Organization, Instr Formats & Modes, Programming the Basic Computer, Input Output Organisation, Register Transfer and Microoperations, Control Unit Design
  9. Section 3 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, SQL, File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control
  10. Section 3 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Process Synchronization
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  12. Section 3 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Minimum Spanning Trees, Shortest Path Algos
  13. Section 3 | Theory Of Computation & Compiler Design: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization
  14. Section 3 | Emerging Trends (AI, Societal Ethics & MS Office): Artificial Intelligence, Emerging Tech Trends, Society, Law & Ethics, MS Office Applications
  15. Section 3 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Maintenance and Configuration Management, Software Testing
  16. Section 3 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  17. Section 3 | OOPS, C++, JAVA, HTML: OOPS with C++, Java, HTML Basics, CSS
  18. Section 3 | Java: Java Fundamentals, Array, String, IO & References
  19. Section 3 | Python: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  20. Section 3 | Digital Electronics: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation
  21. Section 3 | Multimedia: Multimedia
  22. BPSC Previous Year Papers:
  23. BPSC Full Mock Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video provides a detailed lecture on the Least Recently Used (LRU) Page Replacement Algorithm, a key concept in operating systems memory management. The instructor begins by defining LRU as a strategy that replaces the page that has not been used for the longest period of time. He contrasts this with the optimal algorithm, suggesting LRU can be viewed as the optimal algorithm looking backward in time rather than forward. The lecture highlights that LRU results in 12 page faults for a specific reference string, which is better than First-In-First-Out (FIFO) replacement. Furthermore, the instructor notes that LRU is a widely used policy that does not suffer from Belady's Anomaly. The second half of the lecture transitions to a whiteboard session where the instructor introduces the concept of "stack algorithms." He explains that LRU and the Optimal (OPT) algorithm belong to this class. He defines a stack algorithm as one where the set of pages in memory for n frames is always a subset of the set of pages in memory for n+1 frames. To illustrate this, he draws a reference string and constructs vertical columns representing memory frames, demonstrating the subset property visually. This comprehensive approach ensures students grasp both the practical application and theoretical underpinnings of LRU.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor starts with a slide titled "Least Recently Used (LRU) Page Replacement Algorithm." He explains the core definition: "Replace the page that has not been used for the longest period of time." He elaborates that this strategy can be thought of as the optimal page-replacement algorithm looking backward in time. The slide displays a reference string and a table showing page frames, indicating that "LRU gives us 12-page faults." The instructor emphasizes that "LRU is much better than FIFO replacement" and states that the LRU policy is often used because it is considered good. He also points out a key advantage: "LRU also does not suffer from Belady's Anomaly." This section sets the theoretical foundation for why LRU is preferred over simpler algorithms like FIFO.

  2. 2:00 – 5:00 02:00-05:00

    The scene shifts to a whiteboard where the instructor addresses the implementation challenges. He writes, "The major problem is how to implement LRU replacement. An LRU page-replacement algorithm may require substantial hardware assistance." He then introduces a specific class of algorithms called "stack algorithms." He writes, "LRU and OPT belong to a class of page-replacement algorithms, called stack algorithms and can never exhibit Belady's anomaly." He provides a formal definition on the board: "A stack algorithm is an algorithm for which it can be shown that the set of pages in memory for n frames is always a subset of the set of pages that would be in memory with n + 1 frames." To make this abstract definition concrete, he writes a long reference string: "7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1" and begins drawing vertical columns to represent memory frames, starting with a single frame containing the number 7. This step-by-step visual breakdown is crucial for understanding the subset property.

  3. 5:00 – 6:22 05:00-06:22

    Continuing the whiteboard demonstration, the instructor builds upon the stack algorithm concept. He draws multiple columns representing different numbers of frames (n, n+1, etc.). For the first column (1 frame), he writes "7". For the second column (2 frames), he writes "7" and "0". For the third column (3 frames), he writes "7", "0", and "1". He continues this process, filling the columns with numbers from the reference string to visually prove the subset property. He draws a column with "2", "0", "3" and another with "4", "0", "3", "3" (or similar variations depending on the specific step). He points to these columns, explaining that the set of pages in the smaller frame count is contained within the larger frame count. This visual proof reinforces the definition of stack algorithms.

The lecture effectively bridges the gap between the theoretical definition of LRU and its practical classification as a stack algorithm. By first establishing LRU's superiority over FIFO and its immunity to Belady's Anomaly, the instructor sets the stage for the more complex concept of stack algorithms. The whiteboard demonstration serves as a crucial visual aid, transforming the abstract mathematical definition of a stack algorithm into a tangible example. This progression helps students understand not just *what* LRU is, but *why* it behaves the way it does, specifically regarding memory frame subsets.

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