Processes that are waiting on other resources, such as a file read, wait on the EVENT data structure. Thus all processes waiting on a single resource wait on a single event. When the resource becomes available, the event is caused, which wakes up all the processes waiting on it. Processes may wait on multiple events for any one of them to happen, including a time out. Events are fully user programmable – that is, users can write systems that use the generalized event system provided by the MCP.