Introduced with Windows 95, DirectX is a high-performance application program interface that hides hardware and operating system characteristics from the application. DirectX is designed to provide high-speed, real-time response to the user interface.
Windows NT 4.0 now includes three DirectX components: DirectDraw, DirectSound, and DirectPlay for Windows NT 4.0 let you run games and other applications designed for DirectX on Windows 95 on Windows NT 4.0 Workstation and Server.
DirectX for Windows NT 4.0 supports the application entry points called by programs designed for DirectX in Windows 95. The functions are implemented differently in Windows NT than in Windows 95, but they allow you to run the DirectX-based programs on a Windows NT 4.0 workstation or server without changes.
The goal for incorporating DirectX in Windows NT was to provide the best possible graphics performance without compromising the robustness of the system. For example, in Windows NT, DirectX functions never communicate directly with hardware; all graphics functions are mediated by the GDI.
DirectDraw for Windows NT 4.0 supports a 32-bit application program interface for accelerated drawing. DirectDraw also can emulate functions by breaking them down into simpler tasks for the hardware, much as GDI does for its clients.
Unlike DirectX for Windows 95, DirectDraw for Windows NT does not communicate directly with the driver or with any hardware. All DirectDraw functions are implemented in Windows NT 4.0 but are mediated by the GDI.
For Windows NT 4.0, DirectSound provides all application entry points for DirectX sound functions. However these functions are emulated and are not in accelerated form.
DirectPlay is a DirectX DLL that simplifies communications between computers, allowing DirectX programs to be run over the network, using a modem, even modem-to-modem. The communications method is hidden from the application and optimized to have minimal effect on the real-time performance of the interface.
DirectPlay for Windows NT 4.0 supports TCP/IP and Novell IPX network protocols on a local area network as well as point-to-point modem connections using TAPI, the Windows Telephony API.