Slider (read/write head)
The tiny air-foil block at the end of the actuator arm that carries the read and write elements and flies nanometres above the platter.
The slider is a small ceramic block, usually AlTiC (alumina–titanium carbide), machined with air-bearing surfaces, that holds the read/write transducers at its trailing edge. In normal operation it never touches the disk; it rides on a cushion of air dragged around by the spinning platter. The lower the slider flies, the finer the bits the head can resolve, so the pursuit of higher areal density has shrunk it for decades — from the 1980s "mini" (100%) through nano, pico and femto to today's even smaller, lighter bodies that track the surface more closely. A slider that touches down is a head crash.