[Solved] Suppose a file system inode has 12 direct pointers, 1 single indirect, 1 double indirect, and 1... If a file size requires accessing the 15th data block, which pointer type is used to locate it? | Operating Systems

Operating Systems - Inode Structure - File Metadata & Block Pointers

Suppose a file system inode has 12 direct pointers, 1 single indirect, 1 double indirect, and 1 triple indirect pointer. If a file size requires accessing the 15th data block, which pointer type is used to locate it?

AThe 15th block is accessed via the 3rd direct pointer

BThe 15th block is accessed via the triple indirect pointer

CThe 15th block is accessed via the double indirect pointer

DThe 15th block is accessed via the single indirect pointer

Step-by-Step Solution

Solution:

Step 1: Count direct pointers coverage
Direct pointers cover blocks 1 to 12.
Step 2: Identify block 15 location
Block 13 onwards are accessed via indirect pointers. Block 15 is the 3rd block in the single indirect block.
Step 3: Confirm pointer type
Single indirect pointer covers blocks after direct pointers up to its capacity, so block 15 is accessed via single indirect.
Final Answer:
Option D -> Option D
Quick Check:
Block 15 is just beyond direct pointers, so single indirect applies [OK]

Quick Trick: Direct pointers cover first 12 blocks; next blocks use single indirect [OK]

Common Mistakes:

MISTAKES

Assuming block 15 is still direct or double indirect immediately

Trap Explanation:

PITFALL

Candidates often miscount block ranges or confuse indirect pointer levels.

Interviewer Note:

CONTEXT

Tests ability to map block numbers to inode pointer types.

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Solution Trace

More Operating Systems Quizzes

If a file size requires accessing the 15th data block, which pointer type is used to locate it?

Step 1: Count direct pointers coverage

Step 2: Identify block 15 location

Step 3: Confirm pointer type

Final Answer:

Quick Check:

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