Directory structure (single-level, two-level, tree, acyclic graph) in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Single-Level Directory Structure

Which of the following best describes a single-level directory structure?

A Files are stored in two separate levels: user and system directories.

B Files are organized in multiple directories with parent-child relationships.

C Directories can have multiple parents, forming a graph structure.

D All files are contained in one directory with no subdirectories.

💡 Hint

Think about how many directories exist and how files are arranged in the simplest structure.

A single-level directory structure has only one directory where all files are stored directly. There are no subdirectories or hierarchy.

📋 Factual

intermediate

Two-Level Directory Structure Characteristics

In a two-level directory structure, what is the main advantage compared to a single-level structure?

A Each user has their own directory, preventing filename conflicts between users.

B It allows files to be shared among multiple users without duplication.

C It supports cycles in directory references for flexible file access.

D It stores all files in a single directory for faster access.

💡 Hint

Consider how user directories help organize files and avoid confusion.

A two-level directory structure creates separate directories for each user, so users can have files with the same name without conflict.

🔍 Analysis

advanced

Tree Directory Structure Benefits

Which of the following is NOT a benefit of a tree directory structure?

A It prevents filename conflicts within the same directory.

B It allows hierarchical organization of files and directories.

C It supports multiple parent directories for a single file.

D It enables easier navigation and management of files.

💡 Hint

Think about the difference between tree and graph structures regarding parent directories.

A tree directory structure does not allow multiple parents for a single directory or file; that is a feature of graph structures.

❓ Comparison

advanced

Comparing Tree and Acyclic Graph Directory Structures

What is the key difference between a tree directory structure and an acyclic graph directory structure?

A An acyclic graph allows directories to have multiple parents, unlike a tree.

B A tree allows cycles, while an acyclic graph does not.

C A tree structure stores files only at the root directory.

D An acyclic graph does not support hierarchical file organization.

💡 Hint

Consider how directories can be linked in each structure.

An acyclic graph directory structure allows directories or files to have multiple parent directories, enabling shared files without duplication, unlike a tree.

❓ Reasoning

expert

Determining Directory Structure Type from Description

A system has directories arranged so that each directory can have multiple parent directories, but no cycles exist. Which directory structure does this describe?

A Single-level directory structure

B Acyclic graph directory structure

C Two-level directory structure

D Tree directory structure

💡 Hint

Think about what structure allows multiple parents but forbids cycles.

An acyclic graph directory structure allows multiple parents for directories or files but does not allow cycles, matching the description.

Practice

1. Which directory structure allows all files to be stored in a single folder without any subfolders?

easy

A. Acyclic graph directory

B. Two-level directory structure

C. Tree-structured directory

D. Single-level directory structure

Solution

1. Step 1: Understand single-level directory

   In a single-level directory, all files are stored in one folder without any subfolders or hierarchy.

2. Step 2: Compare with other structures

   Two-level and tree structures have multiple folders or subfolders, and acyclic graph allows shared folders, so they are not single-level.

3. Final Answer:

   Single-level directory structure -> Option D

4. Quick Check:

   Single-level = all files in one folder [OK]

Hint: Single-level means one folder only, no subfolders [OK]

Common Mistakes:

• Confusing single-level with two-level structure
• Thinking tree structure is single-level
• Assuming acyclic graph is single-level

2. Which of the following correctly describes a two-level directory structure?

easy

A. All files are stored in one directory without subdirectories

B. Directories form a hierarchy with multiple levels

C. Each user has a separate directory under the root directory

D. Directories can share subdirectories forming cycles

Solution

1. Step 1: Recall two-level directory structure

   In two-level structure, each user has their own directory under a common root directory.

2. Step 2: Eliminate incorrect options

   All files are stored in one directory without subdirectories describes single-level, B describes tree structure, and D describes cyclic graphs which are not allowed.

3. Final Answer:

   Each user has a separate directory under the root directory -> Option C

4. Quick Check:

   Two-level = user directories under root [OK]

Hint: Two-level means root plus user folders only [OK]

Common Mistakes:

• Mixing two-level with single-level structure
• Thinking two-level allows deep folder trees
• Confusing acyclic graph with two-level

3. Consider a tree-structured directory where the root has two subdirectories: Docs and Images. Docs contains files a.txt and b.txt. Images contains pic1.jpg. How many total files are in the directory tree?

medium

A. 3

B. 2

C. 4

D. 1

Solution

1. Step 1: Count files in Docs directory

   Docs contains two files: a.txt and b.txt, so count is 2.

2. Step 2: Count files in Images directory

   Images contains one file: pic1.jpg, so count is 1.

3. Step 3: Add all files

   Total files = 2 (Docs) + 1 (Images) = 3 files.

4. Final Answer:

   3 -> Option A

5. Quick Check:

   2 + 1 = 3 files [OK]

Hint: Add files in all subdirectories for total count [OK]

Common Mistakes:

• Counting directories as files
• Forgetting to add files from all subdirectories
• Miscounting number of files in Docs

4. A directory structure is supposed to be a tree, but a user accidentally creates a cycle by linking a subdirectory back to its ancestor. What problem does this cause?

medium

A. The directory structure is no longer acyclic, causing infinite loops

B. Files become inaccessible due to missing links

C. The directory becomes single-level

D. The directory structure automatically corrects itself

Solution

1. Step 1: Understand tree and cycle concepts

   A tree directory must not have cycles; linking back creates a cycle.

2. Step 2: Identify consequences of cycle

   Cycle causes infinite loops when traversing directories, breaking acyclic property.

3. Final Answer:

   The directory structure is no longer acyclic, causing infinite loops -> Option A

4. Quick Check:

   Cycle breaks acyclic tree causing infinite loops [OK]

Hint: Cycles cause infinite loops in directory traversal [OK]

Common Mistakes:

• Thinking files become inaccessible immediately
• Assuming directory fixes cycle automatically
• Confusing cycle with single-level structure

5. In an acyclic graph directory structure, a file can appear in multiple directories by sharing links. Which advantage does this provide compared to a tree structure?

hard

A. It prevents any file from being deleted accidentally

B. It reduces disk space by storing one copy with multiple references

C. It forces all files to be stored in a single directory

D. It creates cycles to speed up file access

Solution

1. Step 1: Understand acyclic graph directory

   Acyclic graph allows multiple directories to share the same file via links, avoiding duplicates.

2. Step 2: Identify advantage over tree structure

   This sharing reduces disk space since only one copy of the file is stored with multiple references.

3. Step 3: Eliminate incorrect options

   Files can still be deleted, it does not force single directory storage, and cycles are not allowed.

4. Final Answer:

   It reduces disk space by storing one copy with multiple references -> Option B

5. Quick Check:

   Shared links save space in acyclic graph [OK]

Hint: Shared links save space by avoiding duplicate files [OK]

Common Mistakes:

• Thinking acyclic graph creates cycles
• Assuming files cannot be deleted
• Confusing with single-level directory