What the operating system does

Students swap webcams and storage under unchanged apps, install a missing driver and grant or refuse an app's camera permission, to explain how the operating system hides hardware from applications and controls access (AC9TDI10K01 node 1).

Security and privacy · How systems are kept safe · about 35 minutes · Open the student lesson

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

Slides Download Present from the browser, or export to PowerPoint or PDF.
Worksheet Download Print the student copy; the Teacher edition has the answers.

Students will be able to

I can explain what the operating system does between apps and hardware.
I can say what a driver is for.
I can explain how the OS controls what apps may use.

Timing

Predict and Try 6 min · Worked example 9 min · Vary 10 min · Practise and Make 10 min

Before class

Try the board yourself.

The one idea: the OS is a layer of abstraction (apps ask for "a camera"; drivers handle each device) and, because it is in the middle, it is the gatekeeper for access. The access idea returns in lesson 3.

Hands-on: show Device Manager (Windows) or System Information (macOS) on a school laptop, and a phone's app permission screen.

Running the lesson

Predict: students who chose "rewrite the app" hold Sam's misconception.
Try: ask what stayed the same and what changed each time.
Worked example: ask who checks the permission, the app or the OS.
Vary: ask why the OS refuses before the camera is even touched.
Make: compare: did anyone give the game camera access, and why not?

The hard part (on purpose)

The layers are invisible in everyday use. Keep pointing at the three rows on the board and ask "who is talking to whom?"

When students get stuck

What you will see	A question to ask	The fix
A student says the app talks to the webcam (Sam's mistake).	Which row does the app's request go to first?	To the OS, which uses the driver.
A student confuses drivers and apps.	Which one would you see on your home screen?	Apps; drivers are hidden inside the OS.

Answers to the checks

a new webcam: You plug in a new brand of webcam. What has to change so your video call app can use it?
The OS needs a driver. The app asks the OS for "the camera", and the OS uses whichever driver matches the webcam plugged in.
Try: swap the hardware: Start the camera, then swap the webcam and start it again. Save a file, swap the storage and save again. Did the apps change?

The apps stayed the same; the OS used a different driver each time. That is the OS hiding the hardware from the apps.
Through the layers: What is a **driver**?
A small program that lets the OS use one particular device
Each device comes with a driver that turns the OS's general requests ("take a picture") into that device's own commands.
Find the mistake: Sam explains why new hardware needs new apps. Click the line where it first goes wrong.
line 2
Line 2: apps ask the OS, and the OS uses the device's driver. A new webcam needs a new driver, not a new app.
The gatekeeper: Because every app has to ask the OS, what else can the OS do?
Decide which apps may use the camera, microphone, files and network
The OS is the gatekeeper: that is why your phone asks "Allow this app to use the camera?"
No driver: Swap to webcam B and start the video call. Webcam B's driver is missing. What happens?

Without a driver, the OS can't use the device, even though it is plugged in.
Driver installed: Install the driver and try again.

With the driver, the same app works.
Refused: Press the Game's camera button. What does the OS do?

The OS refused: Game has no permission to use the camera.
Allowed: Allow Game to use the camera and try again.

Now the OS lets Game through. Only give an app permissions it really needs.
Saving anywhere: Your school laptop saves files to the internal drive or a USB stick, and the Save button looks the same either way. Why?
The app asks the OS to save; the OS uses the right driver for each
The OS hides the difference, so every app saves the same way.
App permissions: A torch app asks for permission to read your contacts. What should you do?
Refuse: a torch doesn't need your contacts
Give each app only the permissions its job needs.
Review: packets: Review: with TCP, what happens when a packet is lost?
It is sent again
The receiver never confirms it, so it is resent.
set up a new computer: Set this computer up: webcam B plugged in and working for the video call, the game NOT allowed to use the camera, and a file saved to the USB stick.

Driver installed, least privilege for the game, and the OS saves to whichever storage is there. Both of the OS's jobs at once.