--- title: "What the operating system does" subtitle: "Security and privacy · How systems are kept safe · Lesson 1" --- # What the operating system does **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** There are thousands of different webcams, and your video call app works with all of them. How? :::teacher-note **In one sentence:** 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). **Students should be able to say:** 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. **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict :::keep-together **You plug in a new brand of webcam. What has to change so your video call app can use it?** ☐ Nothing at all: every webcam works the same inside ☐ The OS needs a driver for the new webcam; the app stays the same ☐ The whole computer must be replaced ☐ The video call app must be rewritten My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** The OS needs a driver. The app asks the OS for "the camera", and the OS uses whichever driver matches the webcam plugged in. ::: ## Run Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Worked example: one request :::keep-together ### Through the layers 1. $\text{app: "start the camera"}$ — The app asks for a camera, not for a particular brand. 2. $\text{OS: is this app allowed?}$ — The OS checks its permissions for that app. 3. $\text{OS} \to \text{driver for webcam B}$ — The OS picks the driver for the webcam that is plugged in. 4. $\text{driver} \to \text{webcam B}$ — The driver sends that device's own commands. 5. $\text{picture} \to \text{OS} \to \text{app}$ — The result comes back up the same way. Now say what a driver is. **What is a **driver**?** ☐ The cable that connects a device ☐ The person using the computer ☐ An app that plays videos ☐ A small program that lets the OS use one particular device ::: :::teacher-note **Answer:** 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. ::: :::keep-together ### Find the mistake **Sam explains why new hardware needs new apps. Click the line where it first goes wrong.** ``` 1 A new brand of webcam is plugged in. 2 The video call app talks straight to the webcam. 3 So the app has to be rewritten for the new webcam. 4 That is why every app needs an update for new hardware. ``` Line: {{field-15}} Why is it wrong? {{lines-2}} ::: :::teacher-note **Answer:** 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. ::: :::keep-together ### The gatekeeper **Because every app has to ask the OS, what else can the OS do?** ☐ Stop the hardware wearing out ☐ Decide which apps may use the camera, microphone, files and network ☐ Make every app faster ☐ Fix bugs in the apps ::: :::teacher-note **Answer:** 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?" ::: :::typical ## Vary: change one thing **No driver.** **Driver installed.** **Refused.** **Allowed.** Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ::: ## The OS :::keep-together ### 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?** ☐ Both drives are the same inside ☐ The app checks which drive it is ☐ The app asks the OS to save; the OS uses the right driver for each ☐ USB sticks pretend to be internal drives ::: :::teacher-note **Answer:** 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. ::: :::keep-together ### App permissions **A torch app asks for permission to read your contacts. What should you do?** ☐ It doesn't matter ☐ Refuse: a torch doesn't need your contacts ☐ Allow it: apps know what they need ☐ Allow it, then uninstall later ::: :::teacher-note **Answer:** Refuse: a torch doesn't need your contacts Give each app only the permissions its job needs. ::: :::keep-together ### Review: packets **Review: with TCP, what happens when a packet is lost?** ☐ The router rebuilds it ☐ Nothing ☐ The whole message restarts ☐ It is sent again ::: :::teacher-note **Answer:** It is sent again The receiver never confirms it, so it is resent. ::: ## Make: set up a new computer Then: on your own phone, find one app with a permission it doesn't need. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ## Exit ticket :::keep-together **Why doesn't a video app need updating when you buy a new webcam? Give one way the OS protects you.** {{lines-3}} ::: :::teacher-note **Answer:** It asks the OS, which uses the new webcam's driver. It decides which apps may use the camera, microphone or files. :::