Input → Processing → Output is the generic model of every computer system, and the very first step of computational thinking: decomposing a problem before you write a single line of code.
| Stage | Question to ask |
|---|---|
| Input | What data enters the system? (from a user, sensor, file, etc.) |
| Processing | What calculations, comparisons or transformations happen to that data? |
| Output | What result leaves the system, and how is it presented? |
| Storage (IPOS) | Does anything need to be saved for later use? |
Problem:“Calculate and display the average of three test marks entered by the user.”
Input
Mark 1, Mark 2, Mark 3
Processing
Add the three marks together, then divide the total by 3
Output
Display the average on the screen
💡 Exam Tip
The most common mistake is placing a calculation in the wrong column — remember, if a step transforms data (adds, compares, sorts, converts), it belongs in Processing, even if it happens right after input is collected.
Question 1
Problem: 'Calculate and display the average of three test marks entered by the user.' Which of these belongs in the INPUT column?
Question 2
Problem: 'Calculate and display the average of three test marks entered by the user.' Which of these belongs in the PROCESSING column?
Question 3
Problem: 'Calculate and display the average of three test marks entered by the user.' Which of these belongs in the OUTPUT column?
Question 4
A vending machine problem: 'Accept coins, calculate change owed, and dispense the item and change.' What is the correct IPO classification of 'calculate change owed'?
Question 5
In the IPO model, what does the 'S' stand for when extended to IPOS?
Question 6
Problem: 'A supermarket till scans a barcode, looks up the price, adds it to the running total, and shows the receipt at the end.' Which step is Input?
Question 7
Why is the IPO model described as a 'generic' model of a computer?
Question 8
Problem: 'A student's final mark is their exam mark (80%) plus their project mark (20%), and the system displays whether they passed (mark >= 50).' Where does 'checking if the mark is >= 50' belong?
Question 9
Problem: 'An ATM reads a card, asks for a PIN, checks the balance, dispenses cash, and updates the stored balance.' Which part is Storage (in the IPOS model)?
Question 10
Problem: 'A library system scans a returned book's barcode, checks if it's overdue, calculates any fine owed, and prints a receipt.' Which step is Output?
Question 11
Problem: 'A thermostat reads the current room temperature, compares it to the target temperature, and turns the heater on or off, then remembers the last setting used.' Which part is Storage?