Understanding device drivers in Operating System/2

To meet its design goals for multitasking, Operating System/2™ requires a device driver architecture for interrupt-driven device management. A device driver in OS/2™ is affected by the new architecture both in its structure and in its relationship to the system. An OS/2 device driver contains components, such as the Strategy Routine and Hardware Interrupt Handler, which have well-defined responsibilities. The basic form of these components is a FAR CALL/FAR RETURN model. The operating system calls the device driver components to handle certain types of events, such as an application I/O request or a device interrupt. In responding to these events, an OS/2 device driver must cooperate with the operating system to preserve system responsiveness by helping to manage the multitasking of concurrent activities. Since OS/2 uses both the real mode and the protected mode of the system processor to support DOS and OS/2 applications, respectively, the components of an OS/2 device driver must execute in both modes. In this manner, an OS/2 device driver can be viewed as an installable extension of the Operating System/2 kernel. Comparisons between IBM Personal Computer DOS and Operating System/2 are drawn to illustrate differences between device management and device driver architecture.