You can also view previously answered questions in the HSW Question Archive . The operating system often recognizes that there is a serious problem and kills off the offending application in a clean way. The other way for a program to crash is for it to take the operating system down with it, meaning that you have to reboot. An application program like Microsoft Word is made up of many layers and components.
Exceptions allow different layers to communicate problems to each other.
For example, say that a program needs some memory, so it asks the operating system to reserve a block of memory. Various layers may continue to throw the exception upward. The operating system then shuts down the program. Well designed software handles all exceptions. As the program needs memory, it requests blocks of memory of specific sizes from the operating system.