In the lesson's model, which direct CPU action is restricted to privileged code?

• Add two values held in ordinary registers
• Change memory-protection control registers
• Compare two values held in ordinary registers

In the lesson's protected user/kernel model, how does an ordinary app save a file?

• Request a file service from the OS
• Issue storage commands without OS checks
• Disable protection and write the disk itself

A program calls a library function that requests a file read from the OS. All execution while handling this call stays in user mode.

Why restrict user programs from changing memory protection or issuing unrestricted device commands?

• Such access could damage another program's data
• Such access would make every request automatically safe
• Such access would remove every need for shared resources

Which sequence follows the lesson's file-read system-call model?

• Read the device first, enter kernel mode, then prepare the request
• Prepare the request, return to user mode, then enter the kernel
• Prepare the request, enter the kernel, handle it, return to user mode

An app has permission to create a folder. A student says this lets the app execute privileged CPU instructions itself. Which correction fits?

• Folder permission lets the app bypass all memory protection
• The app requests a service; the kernel performs protected work
• Folder permission makes all the app's later execution kernel code

An empty desktop disk will hold ordinary office apps that require OS services. What should be installed before those apps?

• A suitable OS providing the services they require
• The office apps so they can create their own OS
• Only a compiler, regardless of the apps' OS requirements

A file-read system call enters the kernel, but the program lacks permission to read the file. Which outcome fits the lesson?

• Kernel entry gives the program permission to read every file
• Kernel entry disables the checks for this particular request
• The kernel can reject the request and return an error