Operating-System Operations

• Modern OSs are interrupt driven. If there are no processes to execute, no I/O devices to service, and no users to whom to respond, an OS will sit quietly, waiting for something to happen.
• Events are almost always signaled by the occurrence of an interrupt or a trap. A trap (or an exception) is a software-generated interrupt caused either by an error (for example, division by zero or invalid memory access) or by a specific request from a user program that an operating-system service be performed.
• With sharing, many processes could be adversely affected by a bug in one program. For example, if a process gets stuck in an infinite loop, this loop could prevent the correct operation of many other processes.
• More subtle errors can occur in a multiprogramming system, where one erroneous program might modify another program, the data of another program, or even the OS itself.