Why are these considered privileged/not privileged?

[whitehorsey]

1. Why are these considered privileged/not privileged?
a. Set value of timer.
b. Read the clock.
c. Invoking a system call
d. Check the current list of running processes


3. a. Yes
b. No
c. Yes
d. No

I'm thinking b/d is not privileged because anyone can have access to it? But I'm not sure what makes a and c privileged.

 

[Simon Bridge]

Think about (c): would you really want just anybody to be able to invoke a system call?
Compare with (b) - does it matter who can read the clock?