My first post here getting ready for op-sys exam and had a few questions the answer to which i cant really find on the web, was wondering if you guys could help me out:

Do I have to go in to kernel mode in order to input/output (programatically), updating the system clock, disabling interrupts, and loading of Load or Limit registers?

Is process Waiting mode just another name for Blocked mode?

And if I initialize a semaphore to negative value, would it have any meaning, or will it be a semaphore that doesnt do anything?