These associations can be formed after the processes have been created and can change dynamically. In UNIX the ordering of processes imposed by their creation order is called the process heirarchy and the dynamic process associations are called process groups. Some systems have both or neither. Signals Signals are OS abstractions of interrupts. They are indications to a process that some asynchronous event has occurred.
Processes can generally define handler procedures that are invoked when a signalis delivered.
Only one process is inthis state on a given processor. The process is ready to run These states may be defined implicitly. A process is in the ready state if its on the ready queue, or blocked if it's on the blocked queue. Frequently there is more than one ready or blocked queue. There may be multiple ready queues to reflect jobs priorities and multiple blocked queues to represent the events for which the process is waiting.