Demand paging in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What happens during a page fault in demand paging?

In demand paging, when a program accesses a page not currently in physical memory, a page fault occurs. What is the immediate action taken by the operating system?

A The OS loads the required page from secondary storage into physical memory.

B The OS terminates the program immediately due to illegal memory access.

C The OS ignores the request and continues execution without loading the page.

D The OS swaps out all pages to free memory before loading the requested page.

💡 Hint

Think about what the OS must do to allow the program to continue after accessing a missing page.

When a page fault occurs, the OS must bring the missing page from disk into physical memory so the program can access it. This is the core mechanism of demand paging.

📋 Factual

intermediate

Which component keeps track of pages currently in physical memory?

In demand paging, which data structure does the operating system use to know which pages are loaded in physical memory?

A Process control block

B File allocation table

C Interrupt vector table

D Page table

💡 Hint

This structure maps virtual addresses to physical addresses.

The page table keeps track of which virtual pages are in physical memory and their frame locations. It is essential for address translation in demand paging.

🔍 Analysis

advanced

Why can demand paging improve system performance?

Demand paging loads pages only when needed. Which of the following best explains how this improves system performance?

A It duplicates pages in memory to speed up access times.

B It preloads all pages before execution, ensuring no delays during program run.

C It reduces the amount of physical memory used by loading only necessary pages, decreasing disk I/O and speeding up execution.

D It disables virtual memory, allowing direct access to physical memory.

💡 Hint

Consider how loading fewer pages initially affects memory and disk usage.

Demand paging loads only pages that a program actually uses, reducing memory consumption and disk reads compared to loading all pages upfront, which can improve overall system responsiveness.

❓ Comparison

advanced

Difference between demand paging and pre-paging

Which statement correctly contrasts demand paging with pre-paging?

A Demand paging loads pages only when referenced; pre-paging loads pages before they are referenced based on prediction.

B Demand paging loads all pages at program start; pre-paging loads pages on demand.

C Demand paging uses no page table; pre-paging uses a page table.

D Demand paging swaps out pages immediately; pre-paging never swaps pages.

💡 Hint

Think about when pages are loaded in each method.

Demand paging waits until a page is needed to load it, while pre-paging tries to predict and load pages before they are accessed to reduce page faults.

❓ Reasoning

expert

What is the impact of thrashing in a demand paging system?

Thrashing occurs when a system spends more time handling page faults than executing processes. What is the main cause of thrashing in demand paging?

A The CPU clock speed is too high, causing rapid page faults.

B The working set of a process is larger than the available physical memory, causing constant page replacements.

C The disk is too fast, leading to excessive page loading.

D The page table is corrupted, causing incorrect page mappings.

💡 Hint

Consider what happens when the memory needed by a process exceeds what is available.

Thrashing happens when a process's working set does not fit in physical memory, causing frequent page faults and excessive swapping, which slows down the system.