Task Initiation, Execution and Termination

Figure 2-1 on page 26 illustrates (in an albeit primitive manner) the application program's dependence on the OS while it's executing. The OS loads the task (i.e., application program) into memory and executes it. While executing, the task may issue calls to the OS requesting performance of various functions. Upon completion, the task returns control back to the OS. The OS then deallocates the memory used by the program and prompts the user for the name of another program to be executed.