Demand paging in Operating Systems - Mini Project: Build & Apply

Understanding Demand Paging

📖 Scenario: You are learning how an operating system manages memory using demand paging. Demand paging loads pages into memory only when they are needed, which helps save memory space.

🎯 Goal: Build a simple step-by-step explanation of demand paging using a dictionary to represent pages and their status, then simulate checking and loading pages on demand.

📋 What You'll Learn

Create a dictionary called pages with page numbers as keys and their status ('not loaded') as values

Create a variable called page_to_load and set it to the page number 3

Write a loop using for page, status in pages.items() to check if page_to_load is in the dictionary and update its status to 'loaded' if it is 'not loaded'

Add a final statement that sets a variable page_status to the status of page_to_load in the pages dictionary

💡 Why This Matters

🌍 Real World

Operating systems use demand paging to efficiently manage memory by loading only the pages a program needs at a given time.

💼 Career

Understanding demand paging is important for roles in system administration, software development, and IT support where memory management concepts are essential.

1

Create the pages dictionary

Create a dictionary called pages with these exact entries: 1: 'not loaded', 2: 'not loaded', 3: 'not loaded', 4: 'not loaded', 5: 'not loaded'.

Operating Systems

# Create the pages dictionary with page numbers 1 to 5 all set to 'not loaded'
pages = {
    1: 'not loaded',
    2: 'not loaded',
    3: 'not loaded',
    4: 'not loaded',
    5: 'not loaded'
}
# Your code here

Need a hint?

Use curly braces to create a dictionary with keys 1 to 5 and all values set to 'not loaded'.

2

Set the page to load

Create a variable called page_to_load and set it to the integer 3.

Operating Systems

pages = {
    1: 'not loaded',
    2: 'not loaded',
    3: 'not loaded',
    4: 'not loaded',
    5: 'not loaded'
}

# Create a variable page_to_load and set it to 3
page_to_load = 3
# Your code here

Need a hint?

Just assign the number 3 to the variable page_to_load.

3

Load the page on demand

Use a for loop with variables page and status to iterate over pages.items(). Inside the loop, check if page equals page_to_load and if its status is 'not loaded'. If both are true, update pages[page] to 'loaded'.

Operating Systems

pages = {
    1: 'not loaded',
    2: 'not loaded',
    3: 'not loaded',
    4: 'not loaded',
    5: 'not loaded'
}

page_to_load = 3

# Use a for loop to check and load the page on demand
for page, status in pages.items():
    if page == page_to_load and status == 'not loaded':
        pages[page] = 'loaded'
# Your code here

Need a hint?

Use a for loop to go through each page and check if it matches page_to_load and is 'not loaded'. Then change its status to 'loaded'.

4

Set the page status variable

Create a variable called page_status and set it to the value of pages[page_to_load].

Operating Systems

pages = {
    1: 'not loaded',
    2: 'not loaded',
    3: 'not loaded',
    4: 'not loaded',
    5: 'not loaded'
}

page_to_load = 3

for page, status in pages.items():
    if page == page_to_load and status == 'not loaded':
        pages[page] = 'loaded'

# Set page_status to the status of page_to_load
page_status = pages[page_to_load]
# Your code here

Need a hint?

Assign the status of the page number stored in page_to_load to the variable page_status.