Hard Disk Drive Design and Technology

Magnetic Hard Disk Drive (page 2)

Get a Hard Drive Data Recovery Quote

Today's magnetic head typically consists of an MR (magneto-resistive) or GMR (giant MR) reading head and a thin-film inductive write head. MR head design is based on the ability of metals to change their resistivity in the presence of a magnetic field. This effect was first found in 1857.

The alloy of Ni and Fe (81%/19%) is widely used in MR heads and is called Permalloy. MR heads are suitable for extremely high bit density and have superior signal-to-noise ratio when compared to inductive read heads. Inductive thin film heads generate strong magnetic fields at the gap between the poles, thereby magnetizing areas of the media.

Continuous improvement of the head design allowed extremely high densities of magnetic recording with magnetic bits getting smaller and smaller. But, the head is only one component of the magnetic recording system, with magnetic media being extremely important as well.

The first magnetic media was called "particulate media" because it included particles of iron oxide (as the magnetic medium) and aluminum oxide (for abrasive resistance). Modern magnetic media is called "thin-film media" and consists of very thin layers with a total thickness about 500 angstroms or 50 nm. The next figure presents a not-to-scale sketch of one of the kinds of thin-film media.

This thin sandwich is usually deposited by physical vapor deposition (when the atoms of different materials are formed on the surface with the minimum of chemical reaction involved) on the metal disk. Magnetic layer is needed to store the data. The reasons for having a thin carbon layer are simple: it increases mechanical durability of the disk and slows down corrosion of the magnetic layer.

This carbon is sometimes called a diamond-like carbon (DLC) since it has similar chemistry to the diamond (both are mostly carbon), it is very hard (Diamond is VERY hard!), and it provides low friction. A thin layer of lubricant on the top is used to minimize the wear of the carbon layer.

Amazingly, but year after year, this super-thin structure gets thinner and thinner to keep the magnetic head flying lower and lower to decrease that magnetic spacing loss...

Page [1] [2] [3] [4] [5] [6]