ASIO

The 1990s Windows audio path ran through the kernel mixer and added hundreds of milliseconds of delay. Fine for system beeps, useless for playing a soft synth live. Steinberg's answer in 1997 was ASIO: the application and the driver share double buffers, and the card signals the moment the next one needs filling. With small buffers, latency drops to a few milliseconds.

ASIO needs the card's manufacturer to write a dedicated driver. For cards without one there is ASIO4ALL, a wrapper that puts an ASIO face on Windows' own drivers. Microsoft eventually responded with WASAPI in Vista, but ASIO remains the studio default. On macOS none of this is needed — Core Audio was built for low latency from day one.