One of the most notable changes inside the magnesium frame is an entirely new mirror mechanism that reduces vibration when flipping up and slamming down.
To show precisely how the redesigned mechanism works, Canon has shared the below video, which uses a 3D rendering of the mechanism to demonstrate how the new design gets the job done.
Similar to the mechanism inside the Canon 7D II, the mirror uses a motor, not a spring, to drive mirror both up and down. This allows the mirror to properly slow down as it reaches the top of the actuation, preventing vibrations like spring-based mirrors have when slamming to a complete stop at full speed.
Overall, the new mechanism means less vibration. It may also mean less wear and tear on your mirror in the long-run. It’s a welcomed addition that we’ll hopefully see in future Canon cameras, such as the yet-to-be-announced 5D Mark IV.