Which power tool is primarily used for drilling holes into hard surfaces?

The hammer drill is primarily designed for drilling holes into hard surfaces, such as concrete and masonry. This tool combines the rotational motion of a standard drill with a hammering action that provides a powerful percussive force, enabling it to break through tough materials. The hammering mechanism effectively drives the drill bit into the surface, making it particularly useful for construction and renovation projects where hard materials are prevalent.

In contrast, the impact driver is typically used for driving screws and fasteners rather than drilling, as it delivers high torque for these applications but lacks the hammering function necessary for penetrating concrete. A saw, on the other hand, is used for cutting materials rather than drilling holes. Lastly, while a rotary tool can be versatile and may include a drilling feature, it is generally more suited for tasks like sanding, grinding, or carving rather than for drilling into hard surfaces effectively. Thus, the hammer drill stands out as the correct answer for this specific function.