Free What the OS does lessonsWhat the OS does · Stage 0 · The operating system's job · Step 3
System calls
How a program legitimately asks the kernel for something, and what happens between the call and the answer. About 12 minutes.
What makes a system call different from an ordinary function call?
- AIt switches the CPU into kernel mode and enters the kernel at a fixed, checked entry point
- BIt is always run on a different CPU core
- CIt is written in a different programming language
Show the answer
It switches the CPU into kernel mode and enters the kernel at a fixed, checked entry point. The mode switch and the single entry point are what give protection.
4 questions on this idea
Short questions that apply the idea to new cases: trace it, work out a number, put steps in order. A wrong answer explains itself.
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