File Allocation Methods: Contiguous, Linked, Indexed Quiz Quiz

This quiz explores key concepts of file allocation methods, including contiguous, linked, and indexed allocation. Strengthen your grasp of file organization, storage efficiency, and the benefits and drawbacks of each method for operating system design and disk management.

1. Contiguous Allocation Characteristics

   Which of the following statements best describes the contiguous allocation method for storing files?

   1. Files are split and stored in non-adjacent blocks linked by pointers.
   2. All files are stored in the same disk block.
   3. Each file occupies a set of consecutive blocks on the disk.
   4. A block stores pointers to all blocks that make up the file.

   Explanation: Contiguous allocation stores each file in a set of consecutive blocks, simplifying access and improving read performance. The second option describes linked allocation, where files can be scattered on the disk. The third option refers to indexed allocation, using a special index block for pointers. The fourth option is incorrect because files cannot all reside in a single disk block.

2. Main Limitation of Contiguous Allocation

   What is the main disadvantage of contiguous allocation when managing files of varying sizes?

   1. Increased seek time for large files
   2. Complexity of maintaining pointers
   3. Wasted space due to fragmentation
   4. Difficulty in random access

   Explanation: Contiguous allocation can lead to external fragmentation, causing wasted space and limiting efficient usage of disk storage. Random access is actually efficient in contiguous allocation, so the first choice is incorrect. Maintaining pointers is usually associated with linked or indexed allocation, not contiguous. Large files benefit from low seek times if stored contiguously.

3. Linked Allocation Explanation

   In linked allocation, how are the blocks of a file connected on disk?

   1. An index table lists all block addresses for each file.
   2. Each file's blocks are stored in sequential order without pointers.
   3. Each block contains a pointer to the next block in the chain.
   4. All file blocks are stored contiguously.

   Explanation: Linked allocation works by storing pointers in each block to the next block of the file, allowing non-contiguous storage. The first and fourth options incorrectly refer to contiguous allocation. The third option is a description of indexed allocation where a table of addresses is used. Hence, only the second option accurately describes linked allocation.

4. Random Access Capability

   Which file allocation method is most suitable for applications requiring fast and direct random access to file blocks?

   1. Sequential allocation
   2. Indexed allocation
   3. Linked allocation
   4. Contiguous allocation

   Explanation: Indexed allocation is best for random access because the index block allows direct access to any file block by its position. Contiguous allocation also allows random access, but is constrained by fragmentation issues. Linked allocation is slow for random access due to the need to traverse pointers. Sequential allocation is primarily for files accessed in order, not for random block retrieval.

5. Example Scenario: Growing Files

   Suppose a file's size increases gradually. Which file allocation method allows for easy growth without moving the file's existing blocks on disk?

   1. Fixed allocation
   2. Contiguous allocation
   3. Indexed allocation
   4. Linked allocation

   Explanation: Linked allocation easily supports file growth because new blocks can be allocated anywhere and linked to the end of the chain. Contiguous allocation may require relocating the entire file due to fragmentation. Indexed allocation supports file growth to an extent but may need a new, larger index block if expanded beyond capacity. Fixed allocation is not an established method and does not address file growth.

6. Indexed Allocation Structure

   In the indexed allocation method, where are the pointers to a file's disk blocks stored?

   1. At the beginning of each block within the file
   2. Randomly scattered throughout the disk
   3. Inside the file’s metadata in the master directory
   4. Within a separate index block assigned to each file

   Explanation: Indexed allocation stores all pointers for a file's blocks in a separate, dedicated index block, making access efficient. Storing pointers at the start of each block is characteristic of linked allocation. Scattering them randomly is inefficient and not practiced, while storing pointers only in metadata would not provide enough space for large files.

7. Fragmentation Concept

   Which type of fragmentation is most commonly associated with contiguous allocation?

   1. External fragmentation
   2. Temporal fragmentation
   3. Internal fragmentation
   4. Logical fragmentation

   Explanation: Contiguous allocation often leads to external fragmentation, where free space becomes broken up into noncontiguous sections, making it hard to find a large block for new files. Internal fragmentation refers to wasted space within allocated blocks. Temporal and logical fragmentation are not standard fragmentation types in this context.

8. Pointer Overhead Issue

   Which file allocation method introduces overhead due to the need for storing many pointers, especially for large files?

   1. Linked allocation
   2. Indexed allocation
   3. Direct allocation
   4. Contiguous allocation

   Explanation: Linked allocation uses a pointer in each block to indicate the location of the next, which increases overhead, particularly for large files. Contiguous allocation requires no per-block pointers. Indexed allocation uses one central index, minimizing pointer storage per data block. Direct allocation is not a standard term and does not specifically address pointer overhead.

9. Seeking and Access Time

   Which allocation method typically results in the slowest sequential access due to the need to follow multiple pointers on the disk?

   1. Contiguous allocation
   2. Indexed allocation
   3. Linked allocation
   4. Striped allocation

   Explanation: Linked allocation is usually slow for sequential access compared to others because each block must be visited in sequence by following pointers, causing extra read operations. Contiguous allocation is fastest since blocks are adjacent. Indexed allocation maps all block addresses at once, speeding up retrieval. Striped allocation is unrelated to standard file allocation schemes covered here.

10. Summary Table Analysis

    Which feature is unique to indexed allocation among the standard file allocation techniques?

    1. Requires external index block
    2. Minimizes external fragmentation
    3. Allows files to grow without moving blocks
    4. Uses pointers within data blocks

    Explanation: Indexed allocation is distinct for using an external index block to store pointers to all file blocks. While it can minimize fragmentation and support growth, linked allocation also supports file growth without moving blocks but does so using pointers in data blocks. Minimizing external fragmentation is shared with linked allocation. Only indexed allocation necessarily requires a separate index block.