Hardware Abstraction Layer (HAL)

DirectDraw provides device independence through the hardware-abstraction layer (HAL). The HAL is a device-specific interface, provided by the device manufacturer, that DirectDraw uses to work directly with the display hardware. Applications never interact with the HAL. Rather, with the infrastructure that the HAL provides, DirectDraw exposes a consistent set of interfaces and methods that an application uses to display graphics. The device manufacturer implements the HAL in a combination of 16-bit and 32-bit code under Windows 95. Under Windows NT, the HAL is always implemented in 32-bit code. The HAL can be part of the display driver or a separate DLL that communicates with the display driver through a private interface that driver's creator defines.

The DirectDraw HAL is implemented by the chip manufacturer, board producer, or original equipment manufacturer (OEM). The HAL implements only device-dependent code and performs no emulation. If a function is not performed by the hardware, the HAL does not report it as a hardware capability. Additionally, the HAL does not validate parameters; DirectDraw does this before the HAL is invoked.