Kernel Streaming (WDM-KS)

The Windows Driver Model in Windows 98 and 2000 brought an audio path in which every application was mixed in KMixer, a kernel component that resampled everything to one shared format and added tens of milliseconds of latency. Kernel Streaming is the interface KMixer itself used to talk to the driver, and applications that spoke to it directly could skip both the delay and the resampling.

It was never meant as a public API for applications, and it showed: documentation was thin and behaviour varied between drivers. It was used anyway by low-latency software and by audiophile players chasing bit-perfect output, often through PortAudio. Windows Vista dropped KMixer, and WASAPI exclusive mode delivered the same benefits in an orderly fashion.