## Virtual Device Driver Reference for OS/2

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### Reserved IRQ Support in OS/2

The OS/2 operating system does not provide support for optional devices on the Reserved and Redirect Cascade interrupt levels in OS/2-mode sessions, or in DOS sessions. Hooking one of these hardware interrupt request levels in a DOS application has no effect. If there is no physical device driver/ virtual device driver pair to service an interrupt, the DOS application's interrupt handler is not invoked, even though the hardware interrupts are generated.

These hardware interrupt request levels can be supported in a DOS session by a user-installed virtual device driver. However, a user-installed physical device driver is also required to provide this support since there is no mechanism for a virtual device driver to directly service a hardware interrupt.