You really should take weeks to read a book about operating systems; I rmend Operating Systems Three Easy Pieces ~remzi . Then read something about puter architecture s & instruction sets s . By definition CPU modes s are designed to protect software (and also protect from italic buggy code). So if you could carelessly switch to ring in arbitrary ways that ring won obey its functions. Unless you found a huge security hole in your hardware (which is unlikely) switching to ring can only happen in a very controlled way. You should learn more about System call s . BTW I rmend to install and use some Linux distribution because it is mostly made of free software s so you can study the source code and understand in details how things happen. Of course you may need dozens of years to understand most details. See also OS Development which gives technical details (useful if you go into the hobby of developing your own hobby OS; but be careful that takes years of work).