The application or applet that initiates an exchange of Apple events is called the client application. The client requests the help of the server (“do something for me!”). The client’s Apple event(s) may request data (e.g., text, database records) or just a sequence of actions that the server should take (“Open a file and send me the paragraph that begins with ‘Top-secret information.’”). The client can also be thought of as the Apple event “source,” and the server can be thought of as a “target.” An application can be both an Apple-event client and a target (if a client receives a reply Apple event, then it’s the target of that event).
A machine can send up to about 2,000 Apple events per second (and can be as pokey as about 5 per second). This speed depends on factors such as how quickly the target application can process the Apple event(s).
Let’s drill down further into Apple events. Section 1.2.4 shows you what an Apple event looks like at the system level, using the sleep Apple event, a Finder command, as an example.