Answer: Hardware acceleration is a process in which we use hardware to perform some functions rather than performing those functions using the software which is running in the CPU.
WPF exploits hardware acceleration in a two tier manner.
WPF API first detects the level of hardware acceleration using parameters like RAM of video card , per pixel value etc. Depending on that it either uses Tier 0, Tier 1 or Tier 2 rendering mode.
Tier 0:- If the video card does not support hardware acceleration then WPF uses Tier 0 rendering mode. In other words it uses software acceleration. This corresponds to working of DirectX version less than 7.0.
Tier 1:- If the video card supports partial hardware acceleration then WPF uses Tier 1 rendering mode. This corresponds to working of DirectX version between 7.0 and 9.0.
Tier 2:- If the video card supports hardware acceleration then WPF uses Tier 2 rendering mode. This corresponds to working of DirectX version equal or greater than 9.0.