Built in focus motors?

Does anybody know if the tamron 17-50 2.8 for nikon has a built in focus motor? How about the sigma 17-50, does the sigma have one? I'm concerned because i have a d5100, which doesn't have a built in motor.

Sigma lenses with the, 'HSM,' designation have motors - Tamron probably have a similar system - consult your dealer.

This is a trusted site and has very thorough item descriptions. Check the lenses one by one here.

http://www.bhphotovideo.com/...era_Lenses