Originally posted by cfraz The 3-motor mechanism was introduced on the K-3.
Actually, it was introduced with the K-7, and redesigned in the K-3. Otherwise, it would not be possible to operate the shutter in Live View or stop down the aperture without cycling the mirror on a K-7 or K-5. The K-x, K-r, K-30, and K-50 have mirror and aperture mechanisms which are linked, which is why the mirror cycles when taking a picture in Live View or after using the depth-of-field preview on these cameras. However, this extra mirror cycling is not necessary and therefore not observed on the K-7, K-5, or K-3.
Pentax's mention of the three-motor design in the K-3 simply refers to a redesigned drive system for faster operation.
--DragonLord