Internal vs external fragmentation in Operating Systems - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Internal Fragmentation

Which of the following best describes internal fragmentation in memory management?

A Memory lost when the system reserves space for the operating system.

B Unused memory space within an allocated block due to fixed block sizes.

C Memory space wasted between allocated blocks due to variable block sizes.

D Memory fragmentation caused by external devices accessing RAM.

💡 Hint

Think about wasted space inside allocated memory blocks.

Internal fragmentation happens when fixed-size memory blocks are allocated, and the process does not use the entire block, leaving some space unused inside the block.

🧠 Conceptual

intermediate

Understanding External Fragmentation

What is external fragmentation in the context of memory allocation?

A Free memory scattered in small blocks between allocated memory chunks.

B Memory fragmentation caused by hardware faults.

C Memory reserved for system processes only.

D Wasted memory space inside allocated blocks.

💡 Hint

Consider how free memory is arranged outside allocated blocks.

External fragmentation occurs when free memory is split into small pieces scattered between allocated blocks, making it hard to allocate large contiguous blocks.

❓ Comparison

advanced

Comparing Internal and External Fragmentation

Which statement correctly compares internal and external fragmentation?

A External fragmentation wastes memory inside allocated blocks; internal fragmentation wastes memory outside allocated blocks.

B Internal fragmentation occurs only in virtual memory; external fragmentation occurs only in physical memory.

C Internal fragmentation wastes memory inside allocated blocks; external fragmentation wastes memory outside allocated blocks.

D Both internal and external fragmentation waste memory inside allocated blocks.

💡 Hint

Think about where the wasted memory is located in each case.

Internal fragmentation is wasted space inside allocated blocks, while external fragmentation is wasted space outside allocated blocks scattered in small free blocks.

🚀 Application

advanced

Identifying Fragmentation Type from Scenario

A system allocates fixed-size memory blocks of 4 KB. A process requests 6 KB, so it gets two blocks (8 KB total). The extra 2 KB in the second block remains unused. What type of fragmentation is this an example of?

A No fragmentation

B External fragmentation

C Both internal and external fragmentation

D Internal fragmentation

💡 Hint

Focus on unused space inside allocated blocks.

The unused 2 KB inside the allocated block is internal fragmentation because it is wasted space inside allocated memory.

❓ Reasoning

expert

Effect of Fragmentation on Memory Allocation

Consider a memory system with many small free blocks scattered between allocated blocks. Which of the following is the most likely consequence?

A Large memory requests may fail despite enough total free memory due to external fragmentation.

B Memory requests always succeed because total free memory is sufficient.

C Internal fragmentation increases as more small blocks are allocated.

D The system automatically merges allocated blocks to reduce fragmentation.

💡 Hint

Think about how scattered free memory affects large allocations.

External fragmentation causes free memory to be split into small pieces, so large requests may fail even if total free memory is enough.

Practice

1. Which of the following best describes internal fragmentation in memory management?

easy

A. Wasted space outside allocated memory blocks

B. Wasted space inside allocated memory blocks

C. Memory lost due to hardware failure

D. Memory used by the operating system kernel

Solution

1. Step 1: Understand internal fragmentation

   Internal fragmentation happens when allocated memory blocks have unused space inside them because the block size is larger than the requested memory.

2. Step 2: Compare with external fragmentation

   External fragmentation is about wasted space outside allocated blocks, so it is different from internal fragmentation.

3. Final Answer:

   Wasted space inside allocated memory blocks -> Option B

4. Quick Check:

   Internal fragmentation = wasted space inside blocks [OK]

Hint: Internal = inside allocated blocks wasted space [OK]

Common Mistakes:

• Confusing internal with external fragmentation
• Thinking fragmentation is caused by hardware
• Mixing up allocated and free memory spaces

2. Which of the following statements about external fragmentation is syntactically correct?

easy

A. External fragmentation wastes space inside allocated blocks.

B. External fragmentation is caused by software bugs only.

C. External fragmentation means memory is fully used without gaps.

D. External fragmentation wastes space outside allocated blocks in free memory.

Solution

1. Step 1: Identify correct definition of external fragmentation

   External fragmentation refers to wasted space outside allocated blocks, scattered in free memory.

2. Step 2: Check other options for correctness

   The statement "External fragmentation wastes space inside allocated blocks" describes internal fragmentation. The claim that it is caused by software bugs only is incorrect, as it arises from repeated allocation and deallocation. The idea that memory is fully used without gaps is false, since fragmentation creates unusable gaps in free memory.

3. Final Answer:

   External fragmentation wastes space outside allocated blocks in free memory. -> Option D

4. Quick Check:

   External fragmentation = wasted free memory gaps [OK]

Hint: External = wasted space outside allocated blocks [OK]

Common Mistakes:

• Mixing internal and external fragmentation definitions
• Assuming fragmentation is only due to bugs
• Ignoring free memory gaps in external fragmentation

3. Consider a memory system where 5 blocks of size 10KB are allocated, but each request was for 8KB. What type of fragmentation is present and what is the total wasted memory?

medium

A. Internal fragmentation; 10KB wasted total

B. Internal fragmentation; 2KB wasted

C. Internal fragmentation; 10KB wasted inside each block

D. External fragmentation; 10KB wasted

Solution

1. Step 1: Calculate wasted space per block

   Each block is 10KB but only 8KB is used, so 2KB is wasted inside each block.

2. Step 2: Calculate total wasted memory

   With 5 blocks, total wasted = 5 blocks * 2KB = 10KB wasted inside allocated blocks, which is internal fragmentation.

3. Final Answer:

   Internal fragmentation; 10KB wasted total -> Option A

4. Quick Check:

   Internal fragmentation = wasted inside blocks total 10KB [OK]

Hint: Wasted inside allocated blocks = internal fragmentation [OK]

Common Mistakes:

• Confusing total wasted with per block wasted
• Mixing internal with external fragmentation
• Ignoring multiplication by number of blocks

4. A system has free memory blocks of sizes 5KB, 3KB, and 4KB scattered around. A process requests 6KB. Which problem is this an example of, and what is the main issue?

medium

A. External fragmentation; no single free block large enough

B. Internal fragmentation; wasted space inside allocated blocks

C. External fragmentation; all free blocks are too large

D. Internal fragmentation; process size is too small

Solution

1. Step 1: Analyze free memory blocks

   The free blocks are 5KB, 3KB, and 4KB. The process needs 6KB, but no single block is large enough (maximum 5KB < 6KB).

2. Step 2: Identify fragmentation type and issue

   Free memory total is 12KB > 6KB, but scattered into small non-contiguous blocks with none large enough, causing allocation failure. This is external fragmentation.

3. Final Answer:

   External fragmentation; no single free block large enough -> Option A

4. Quick Check:

   External fragmentation = scattered free blocks too small [OK]

Hint: External fragmentation = scattered free blocks too small [OK]

Common Mistakes:

• Confusing internal with external fragmentation
• Assuming process size is too small causes fragmentation
• Ignoring block sizes when allocating memory

5. A system uses fixed-size memory blocks of 4KB. A program requests 10KB. How does internal and external fragmentation affect this allocation, and what is the total wasted memory?

hard

A. Internal fragmentation wastes 4KB; external fragmentation wastes 2KB

B. Internal fragmentation wastes 2KB; external fragmentation wastes 4KB

C. Internal fragmentation wastes 2KB; external fragmentation wastes 0KB

D. Internal fragmentation wastes 0KB; external fragmentation wastes 2KB

Solution

1. Step 1: Calculate blocks needed and internal fragmentation

   10KB requires 3 blocks of 4KB each (total 12KB). The extra 2KB (12KB - 10KB) inside allocated blocks is internal fragmentation.

2. Step 2: Consider external fragmentation

   Since blocks are fixed and allocated contiguously, no free space outside allocated blocks is wasted here, so external fragmentation is 0KB.

3. Final Answer:

   Internal fragmentation wastes 2KB; external fragmentation wastes 0KB -> Option C

4. Quick Check:

   Internal fragmentation = 2KB; external = 0KB [OK]

Hint: Internal = leftover in allocated blocks; external = gaps outside [OK]

Common Mistakes:

• Miscounting blocks needed for allocation
• Confusing internal and external fragmentation amounts
• Assuming external fragmentation always occurs