Hammer drill VS Rotary hammer
The hammer drill vibrates in and out very fast to make masonry drilling much easier.
Rotary hammers are drills with a piston on the inside which is operated by the motor and gears. When the motor turns, it moves a gear, which then moves a rod. The rod hits a hammer mechanism which transfers the strike force into the rotary hammer bit. All of this happens very rapidly. Because there is a piston being struck, the force of the blow against the bit is much harder than that of a hammer drill.
Hammer drills have a motor that turns a splined gear type mechanism inside the tool. These splined gears are meshed together and hit against each other creating a vibrating action that is transferred to the drill chuck and bit. The hammering is rapid, but the force is only a fraction of that delivered by a rotary hammer.