## Virtual Device Driver Reference for OS/2

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### Virtual Parallel Port Device Driver

The virtual parallel port device driver (VLPT) consists of virtual support for direct hardware access to the three parallel ports (LPT1, LPT2, and LPT3), and for the printer-related BIOS entry points (Printer I/O INT 17h, Print Screen INT 05h). Existing DOS applications that access the parallel ports, either by direct access to the ports or by printer BIOS, operate without change. The VLPT provides the virtualization to allow multiple DOS applications to access virtual printer hardware simultaneously. This virtual device driver, in conjunction with the spooler, attempts to prevent multiple DOS applications that transmit data by using BIOS functions or direct hardware access, from intermixing output at the parallel port.

The virtual parallel port device driver consists of several sections:

BIOS INT 17h Emulation
BIOS INT 05h Emulation
Printer Close Processing
Direct I/O Access