HD (Hard Drive) Question:

★ In a hard disk information / data is written on the rotating platters by the read and write heads.
★ The heads are not in actual contact with the disk they are actually slightly above the magnetic surface of the platter.
★ The heads detects the magnetization of the platter right below them. The actuator arm aids the heads in covering the platter area.
★ The surface is divided into micro sized areas known as magnetic domains. Every magnetic domain has a magnetic dipole which has their own field.
★ The write heads read/write by magnetizing the area. It generates a strong magnetic field for this purpose.