## Input/Output Device Driver Reference

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### Virtual Device Drivers

The virtual device driver is an installable module that virtualizes a particular piece of hardware and associated ROM BIOS in the manner expected by a DOS application. This device driver achieves virtualization by emulating I/O port and device memory operations. Virtual device drivers are 32-bit device drivers that operate at Ring 0. To achieve a certain level of hardware independence, a virtual device driver usually communicates with a physical device driver in order to interact with hardware.

Further information on virtual device drivers, virtual device driver interfaces (including detailed descriptions of the calling conventions), and the system services available to these drivers is found in the OS/2 Virtual Device Driver Reference.