Multitasking can be used so that communication activity can occur while waiting for other activity, such as disk I/O processing, to be completed (see Figure 1). For example, a VTAM® application program can be organized into a task that opens and closes the ACB and performs VTAM requests, and a task that performs disk I/O requests (using VSAM, for example). In such a program, a page fault in the task that performs disk I/O requests does not prevent the task that performs communication requests from getting control during the time that the system is waiting for the required page to arrive in main storage. For a single-task VTAM application program, a page fault in that task would require that the entire program wait.