I recently asked myself: If a program, like Mozilla Firefox for example, is started - the control must be somehow given to it. But when the program crashes, why doesn't my whole system crash like in early Windows version?

• How can Windows take back the control from the program, or even not give it to it fully?

(Note: This is not my homework; I go to school but in my informatics class are really only guys that would answer with "Can I eat that?" when I ask them about kernels. Same with my teacher.)