An average computer user knows what a hard disk drive is for. If asked, an ordinary user would say that it is used to store data. Not everyone knows how a hard drive works much less understand its mechanism.

A hard disk drive (HDD) or simply hard drive is a non-volatile device used for storing data using a magnetic surface on platters.

The hard disk platters are rigidly constructed and each one has a planar magnetic surface where digitized data can be stored. Information is written on the magnetic surface through an electromagnetic flux via an antennae positioned near a magnetic material that has a polarization that changes. The stored data can be read by a read-write head that senses electrical change when the magnetic fields pass close to the rotating platter.

A typical design of a hard drive consists of a central spindle from which the platter spins constantly. Then there are the read-write heads that moves along and in between the platters in a radiating direction that allows the many heads (one for each platter) to cover the entire platter.

The movement of the read-write armature is controlled by complex electronics. The disk controller electronics also perform reads and writes as needed and schedule read and write tasks on demand as well as the remapping of failing hard drive sectors.

The SMART technology is also supported by major hard drive models. This technology prevents data loss by warning the user. Data loss is also avoided by the external protection provided by a sealed enclosure. But this structure is specifically made to protect the internal structure from dust, condensation, and other sources of contamination. The internal mechanism of the hard drive is so sensitive so keeping them stable from external forces is very important. The read-write head fly on a cushion of air only nanometers above the surface of the disk.

A mistaken belief of most users is that a hard drive has a vacuum. Actually, the system of the hard drive relies on air pressure inside the structure to support the heads during “flight” or reading-writing tasks. Users also assume that hard drives are totally sealed, but hard drives to work correctly needs a range of air pressure. If too low, it will not exert force on the heads or keep them at the proper height.

Hard drives have permeable filters located between the inside of the drive and the top cover. This allows moisture in the air outside to enter the drive. These filters can be seen as breather holes and usually has stickers to warn the user not to cover them.