The hard drive uses two important principles about the magnetic fields. :: Computer Science

The hard drive uses two important principles about the magnetic fields. When we write data onto the hard drive Cit uses the law of electromagnetic induction and some material is magnetic. The hard drive uses two important principles about the magnetic fields. When we write data onto the hard drive it uses the law of electromagnetic induction and some material is magnetic. When we read data from the hard drive, it uses the Lenz's law. How hard disk drive works: Firstly we should know the two important part of the hard disk drive, 1. platters and media We put all of the data onto the platters. They are inside of the hard drive. There are several pieces of platter in the hard disk drive, maybe three or four. They are made of special material. The material must be strong and light. Because there are high rotation rates, when the hard disk drive working. Traditionally, people often use aluminum because it is a light material. But today, most platters are made from material like glass or ceramic composite. These light, strong materials have a very low thermal expansion, and compare to aluminum. They can withstand higher forces. So the platters can run faster. Older hard disk drive can only run at 3600 to 5200 rpm. Today's ones can run7600 to 10000 rpm. There is a layer of magnetic material on the surface of the platters. Today a thin-film media is used here. Thin-film media is a microscopic layer of pure metal bonded to the substrate surface through an interim layer. Because the distance between head and platters is very small (about 10 micro inches), but they can not touch with each other. So the thin-film media is very flat and is coated with a protective layer to help survive head crashing. 2. the arm and read and write head The arm that holds the read/write heads is controlled by the mechanism in the upper-left corner, and is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast. The arm on a typical hard-disk drive can move from hub to edge and back up to 50 times per second. It is hard to believe. But it is the truth. Simply, The read and write head is a ferromagnetic core. It can product a variety magnetic fields through a variety current to be able to write data onto the media in ASC2. And also can product variety current though inducing the variety magnetic field on the surface of the platter to read data from the hard disk drive.