## Virtual Device Driver Reference for OS/2

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### Access to Ports Not Trapped by a Virtual Device Driver

In order to support DOS applications that use hardware that does not have virtual device drivers, a mechanism is provided for DOS applications to access ports on those devices. This is done by having the default handler for each I/O port turn trapping OFF for the port in question. All accesses after the first one go straight through to the hardware. This is done only for ports that are not trapped by a virtual device driver.