iAPX 286 Operating System Writers Guide 1983

111'eI INTRODUCTION TO PROTECTED MULTITASKING ON THE iAPX 286GLOBAL SPACE11~'1,~1. ~~~~:~NGD A~PLlCATIONTASKB121960-43Figure 1-4. A Four-Level Protection Structureof the system. Because many I/O functions involve waiting for responses from I/O devices, it is mostconvenient to treat these functions as a separate task that can run asynchronously with respect to thetasks that invoke them. Figure 1-7 illustrates a structure with independent operating-system tasks.ROLE OF THE OPERATING SYSTEMThe role that an operating system may play in managing a multitasking execution environment dependson the nature of the application. Applications can be classified according to the volatility of tasks1-6 121960-001