Close-up of an actuator arm of a hard disk drive, a device to store and retrieve digital information. Four read/write anisotropic magnetoresistive heads (AMR) move above the two disk platters (a spindle motor spins the disks at high speed). They have a magnetic coating which transforms the platter's magnetic field into electrical current when reading the disk, and which turns the electrical current into a magnetic field when writing the disk with the write transducer. An actuator arm made of neodymium-iron-boron, positions the read/write head assembly across the spinning disks. The heads 'fly' above the disk surface with a clearance of a few nanometres, controlled by the design of an air-bearing, etched onto the disk-facing surface of the slider. Field of view size: 12.5 x 18.9 mm (0.50 x 0.75 in)