Application crashes - occur within a single process, and do not always affect the system and other applications. Crash detection and recovery varies according to the type of crash and the choice of hardware. They use software to program the hardware and to restart the system if a critical application fails or quits unexpectedly. System Crashes System crashes occur at a very low level, causing all applications to freeze and the entire system to come to a halt. When crashed, the system does not respond to software commands and the Finder's Restart command cannot be executed.
Recovery requires external intervention.
While the system is running normally, highly integrated communication is continuous between the our software and our hardware. System crashes are detected when there is a disruption of the background communication between the our software and our hardware. Our software periodically sets and updates an internal system timer in our hardware. When the system crashes, the software cannot update the hardware timer. When the timer expires, the hardware will restart the computer.