Microsoft Windows Network Virtual Device Drivers

This document describes the function and implementation of two network virtual device drivers—VDNET.386 (DECnet) and VNETBIOS.386 (NetBIOS)—included in Digital's PATHWORKS for DOS version 4.1. It explains how these drivers, which operate only in Windows enhanced mode, provide a necessary bridge between Windows applications running in protected mode and DOS real-mode applications. Key topics include the Windows enhanced mode environment, processor operating modes (real, protected, and virtual), how virtual device drivers virtualize hardware ports and interrupts, and how they handle communication between protected and real-mode applications via API mapping and asynchronous operations.