How a Computer Hard Drive Works

We hear the whir of our computer every day but rarely stop to ask, “How does our computer work?” The brains of our computer lie within the hard drive. These components, once only holding 20 megabytes which was considered sizeable, can now hold as much as 3 terabytes of information. How a hard drive functions to hold all this data is quite impressive.

Parts of a hard drive

A computer hard drive consists of a spindle that holds platters  Held on these platters is all of the stored information. Platters are made out of a non-magnetic material such as glass, ceramic, or an aluminum alloy and then coated with a very thin layer of a magnetic material. The platters spin at speeds of anywhere from 4,200 rpm to 15,000 rpm depending upon the performance of the computer. Also part of a hard drive are two motors—one that spins the platters and one called an actuator that moves a read-write head on the platter. This read-write head is supported by a head support arm which allows the head to reach acceleration speeds of 550 Gs.        

How the hard drive works

A hard drive stores information by magnetizing ferromagnetic material on the platters.  Changes in the magnetization direction denote binary data bit patterns. These are read when the changes are detected by the read-write head as it passes over the platter. This head both detects the magnetization and has the capability to modify it, hence “writing.”  This is done by generating a strong local magnetic field. The head never actually touches the spinning platter; a very small layer of air that moves at the speed of the platter keeps them from touching. When a request for data is made, the location of this data on the platter is found in the registry of the hard drive. When it is located, the head is directed to the correct location on the platter to retrieve the information.