Paging concept and page tables in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the purpose of paging

What is the main purpose of using paging in an operating system?

A To divide physical memory into fixed-size blocks called frames and map them to pages in virtual memory

B To increase the size of the CPU cache for faster processing

C To encrypt data stored in memory for security

D To allow direct access to hardware devices without OS intervention

💡 Hint

Think about how memory is managed to avoid fragmentation and simplify allocation.

Paging divides physical memory into fixed-size frames and virtual memory into pages. This allows the OS to map pages to frames flexibly, avoiding fragmentation and simplifying memory management.

📋 Factual

intermediate

Page table entry contents

Which of the following is NOT typically stored in a page table entry?

A Frame number where the page is stored

B Validity bit indicating if the page is in physical memory

C Process ID of the owner process

D Access permissions like read or write

💡 Hint

Consider what information is needed to translate virtual addresses to physical addresses.

Page table entries store the frame number, validity bit, and access permissions. The process ID is managed elsewhere, not in the page table entry.

🔍 Analysis

advanced

Calculating page table size

An operating system uses 32-bit virtual addresses and a page size of 4 KB. How many entries does a single-level page table have?

A 65,536 entries

B 1,048,576 entries

C 262,144 entries

D 4,096 entries

💡 Hint

Calculate the number of pages by dividing the virtual address space by the page size.

Virtual address space is 2^32 bytes. Page size is 4 KB = 2^12 bytes. Number of pages = 2^(32-12) = 2^20 = 1,048,576 entries.

❓ Comparison

advanced

Difference between internal and external fragmentation

Which statement correctly distinguishes internal fragmentation from external fragmentation in memory management?

A External fragmentation occurs only in virtual memory; internal fragmentation occurs only in physical memory.

B External fragmentation happens inside allocated blocks; internal fragmentation is caused by scattered free blocks.

C Internal fragmentation is caused by paging; external fragmentation is caused by segmentation only.

D Internal fragmentation occurs when allocated memory blocks have unused space; external fragmentation is free memory scattered in small blocks.

💡 Hint

Think about wasted space inside allocated blocks versus scattered free space outside allocated blocks.

Internal fragmentation is wasted space inside allocated memory blocks due to fixed block sizes. External fragmentation is free memory scattered in small pieces that can't be used effectively.

❓ Reasoning

expert

Effect of page size on page table size and fragmentation

How does increasing the page size affect the size of the page table and the amount of internal fragmentation?

A Page table size decreases and internal fragmentation increases

B Page table size increases and internal fragmentation decreases

C Both page table size and internal fragmentation increase

D Both page table size and internal fragmentation decrease

💡 Hint

Consider how page size affects the number of pages and leftover space inside pages.

Larger page size means fewer pages, so the page table has fewer entries (smaller size). But larger pages cause more unused space inside pages, increasing internal fragmentation.