DirectSound accesses the sound hardware through the DirectSound hardware-abstraction layer (HAL), an interface that is implemented by the audio-device driver. This is a Windows audio-device driver that has been modified to support the HAL. This driver architecture provides backward compatibility with existing Windows-based applications. The DirectSound HAL provides the following functionality:
·Acquires and releases control of the audio hardware
·Describes the capabilities of the audio hardware
·Performs the specified operation when hardware is available
·Fails the operation request when hardware is unavailable
The device driver does not perform any software emulation; it simply reports the capabilities of the hardware to DirectSound and passes requests from DirectSound to the hardware. If the hardware cannot perform a requested operation, the device driver fails the request and DirectSound emulates the operation.
If a DirectSound driver is not available, DirectSound communicates with the audio hardware through the standard Windows 95, Windows NT®, or Windows 3.1 audio-device driver. In this case, all DirectSound features are still available through software emulation, but hardware acceleration is not possible.