It's a Avid BBDB (Ball Bearing Disc Brake) Type F.
It was the first of the "BB7" models and was made from around 1999 to 2001.
The pads on this model were held in place by magnets on the pressure feet.
Remove one pad at a time, push the pad away from the pressure foot and then pull it out with a pair of pliers, the pressure feet have a protruding bit in the middle which fits into a hole in the pad backing plate.
Avid BBDB Service Manual: http://my-sport.spb.ru/manual_1/ball%20bearing%20disc%20brakeservice%20guide.pdf