Linked File Allocation

Duration: 7 min

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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++
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  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
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  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 lecture introduces Linked Allocation as a file system method that solves the problems associated with contiguous allocation. The instructor explains that with this method, each file is treated as a linked list of disk blocks, which can be scattered anywhere on the physical disk. A key feature is that the directory contains pointers to both the first and last blocks of the file. The video covers the advantages, such as the elimination of external fragmentation and the ability for files to grow dynamically without pre-allocating a fixed size. It also details significant disadvantages, including the overhead of storing pointers, the inability to perform efficient random access, and reliability concerns if a pointer is damaged.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor begins by presenting a slide titled "Linked Allocation" which states that this method solves all problems of contiguous allocation. He explains that with linked allocation, each file is a linked list of disk blocks, and these blocks may be scattered anywhere on the disk. A diagram of a disk cylinder is shown with blocks numbered 0 through 31. The instructor points to a directory entry for a file named "jeep", which has columns for "file", "start", and "end". He traces a path through the blocks (1 -> 6 -> 10 -> 14 -> 18 -> 22 -> 26) to demonstrate how the blocks are linked together. He emphasizes that the directory contains a pointer to the first and last blocks of the file, allowing the system to traverse the entire file. The slide text reads: "The directory contains a pointer to the first and last blocks of the file."

  2. 2:00 – 5:00 02:00-05:00

    The lecture transitions to the advantages of linked allocation. The instructor explains that to create a new file, one simply creates a new entry in the directory. Each directory entry has a pointer to the first disk block of the file. To read a file, the system simply reads blocks by following the pointers from block to block. A major advantage is that the size of a file need not be declared when the file is created; a file can continue to grow as long as free blocks are available. He highlights that there is no external fragmentation with linked allocation, and any free block on the free-space list can be used to satisfy a request. He draws abstract linked list nodes to visualize the structure, reinforcing that blocks are linked sequentially regardless of physical location. The slide text reads: "There is no external fragmentation with linked allocation, and any free block on the free-space list can be used to satisfy a request."

  3. 5:00 – 7:04 05:00-07:04

    The instructor discusses the disadvantages of linked allocation. He notes that to find the i-th block of a file, one must start at the beginning of that file and follow the pointers until reaching the i-th block. Each access to a pointer requires a disk read, which is slow. Another disadvantage is the space required for the pointers, so each file requires slightly more space than it would otherwise. Reliability is also a problem; if a pointer is lost or damaged, the file chain is broken. He suggests partial solutions like using doubly linked lists or storing the file name and relative block number in each block, but notes these schemes require even more overhead. He draws a simple linked list diagram to illustrate the pointer chain. The slide text reads: "Yet another problem is reliability. Recall that the files are linked together by pointers scattered all over the disk, and consider what would happen if a pointer were lost or damaged."

The video provides a comprehensive overview of Linked Allocation in file systems. It begins by defining the concept and illustrating it with a disk diagram and directory structure. The instructor then details the advantages, such as eliminating external fragmentation and allowing dynamic file growth. Finally, he addresses the disadvantages, including slow random access, pointer overhead, and reliability issues, while proposing potential solutions like doubly linked lists. This progression helps students understand the trade-offs involved in file system design.

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