OS + Kernel mode video

Question 1

What does the mode bit do?

Answer 1

If set to one, the processor is in privilege mode/kernel mode and can use any instruction in the instruction set.

If set to zero, instruction use is limited in restricted mode/user mode.

Question 2

How can a mode bit be flipped to one?

Answer 2

An interrupt

Question 3

Can user mode interact with io devices? (graphics card, disc etc.)

Answer 3

No, only kernel mode

Question 4

What happens if an infinite loop occurs within a system call? Does the processor just get stuck?

Answer 4

No, a timer on the hardware level sends an interrupt once it reaches zero to prevent this scenario.

Question 5

How do drivers work?

Answer 5

They run in kernel mode “along side” the OS.

Question 6

Why do devices like GPU’s need drivers?

Answer 6

OS developers can’t optimize/account for every single device. Drivers fix that

Question 7

What are the benefits of using system calls?

Answer 7

Hardware abstraction, Security, Portability

Question 8

What are the cons of system calls?

Answer 8

Performance overhead, platform dependency