File allocation methods (contiguous, linked, indexed) in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Contiguous File Allocation

Which of the following best describes the main characteristic of contiguous file allocation?

A Files are compressed and stored in a single block to save space.

B Files are stored as linked blocks scattered anywhere on disk, with pointers connecting them.

C Files are stored in an index block that contains pointers to all file blocks, allowing random access.

D Files are stored in consecutive blocks on disk, making access fast but causing external fragmentation.

💡 Hint

Think about how the file blocks are arranged physically on the disk.

Contiguous allocation stores all file blocks next to each other on disk. This allows fast sequential access but can cause external fragmentation because free space may be split into small pieces.

📋 Factual

intermediate

Linked Allocation Characteristics

What is a key disadvantage of linked file allocation compared to contiguous allocation?

A It requires a large index block to store pointers to all file blocks.

B It has slower access time because each block contains a pointer to the next block, requiring sequential traversal.

C It causes external fragmentation due to scattered file blocks.

D It cannot handle files larger than a fixed size.

💡 Hint

Consider how the system finds the next block in linked allocation.

Linked allocation stores file blocks anywhere on disk with pointers linking them. Accessing a block requires following pointers sequentially, which slows down random access compared to contiguous allocation.

🔍 Analysis

advanced

Indexed Allocation Advantages

Why does indexed file allocation improve random access compared to linked allocation?

A Because an index block contains pointers to all file blocks, allowing direct access to any block without traversal.

B Because all file blocks are stored contiguously, making access direct.

C Because it compresses file data to reduce disk usage.

D Because it uses a linked list of blocks, reducing overhead.

💡 Hint

Think about how the system finds a specific block in indexed allocation.

Indexed allocation uses a special index block that holds pointers to all the file's blocks. This allows the system to jump directly to any block, improving random access speed compared to linked allocation.

❓ Comparison

advanced

Comparing Fragmentation in Allocation Methods

Which file allocation method is most prone to external fragmentation, and why?

A Contiguous allocation, because files require consecutive free blocks which may not be available as disk fills up.

B Linked allocation, because pointers cause blocks to scatter randomly.

C Indexed allocation, because the index block can become fragmented.

D None of the methods cause external fragmentation.

💡 Hint

Consider how each method allocates space and what happens when disk space is fragmented.

Contiguous allocation needs consecutive free blocks for a file. Over time, free space breaks into small pieces, causing external fragmentation. Linked and indexed methods do not require consecutive blocks, so they avoid this problem.

❓ Reasoning

expert

Choosing File Allocation for Large Files with Random Access

A system needs to store very large files and allow fast random access to any part of the file. Which file allocation method is best suited, and why?

A Contiguous allocation, because it stores files in consecutive blocks for fast access.

B Linked allocation, because it uses pointers to link scattered blocks, saving space.

C Indexed allocation, because it uses an index block to directly access any file block, supporting large files and fast random access.

D None of these methods support large files with random access efficiently.

💡 Hint

Think about how each method supports random access and file size limits.

Indexed allocation supports large files by using an index block that points to all file blocks. This allows direct access to any block, making random access fast even for large files. Contiguous allocation struggles with large files due to fragmentation, and linked allocation is slow for random access.