Normal Recording V/S Perpendicular Recording.

With reference to my previous article on “An Alternate Solution to Hard Drive Recording”, I would now want to explain u’ll how this fascinating technology works.
1)Write Element:
The write element is the head and it is basically an electromagnet which when supplied with current, generates a magnetic field that changes the north and south of the tiny particles on the writing medium (this is how the data is written in the drive). In the longitudinal magnetic recording system, the magnetic field that is generated by the electromagnet has a higher longitudinal component than the perpendicular component.

“Longitudinal component means the strength of the electromagnetic force is greater in the direction that is longitudinal or parallel to the axis of the magnetic medium on the hard disk platter.”

In PMR (Perpendicular Magnetic Recording) the tiny magnets on the recording media are magnetically oriented in the north south direction. To achieve efficient writing in the limited area that is covered by the magnets with the changed orientation, a PMR write head needs to generate magnetic fields in such a way that the perpendicular components are than the longitudinal components.
A “single pole” PMR head combined with a soft-under-layer (SUL) offers a strong perpendicular write field, while the longitudinal component is much reduced making the magnetic field more intense and focused.
Rather than being generated from the gap between the two electromagnets, the field from a PMR write-head is generated from the pole surface and collected by the SUL.
The corners of a rectangular pole will cut into neighboring tracks when the head is operating at a skew angle.
In modern drives, the head has a skew angle with respect to the track direction when the head operates at the inner or outer radii of the magnetic medium. Fabricating a narrow trapezoidal pole with a well-controlled angle is essential l to prevent the fields from the pole surface erasing data in neighboring tracks.

2)Recording Medium:
The recording medium used here is a type of “granular” media, comprised of magnetic alloys containing cobalt, chromium, platinum (CoCrPt) and an oxide grain-boundary segregant. The smaller size allows writing of more data in less space. This material is highly coercive means that the alloy is a magnetically stronger medium. This makes a distinct advantage as it becomes capable of retaining the magnetic charge even when there are high thermal variations inside the hard drive.
In other words this medium provides better areal density which in turn provides more storage!!

3)Soft Under layer:
The unique feature noted about this recording technique is the “Soft Magnetic Under layer” incorporated into the disk. This under layer conducts the magnetic flux very easily.

“Magnetic flux is the unit of measurement of the strength as well as the range of the magnetic field.”

When a current is passed through the writing head, flux concentrates under the small pole-t ip and generates and intense magnetic field in the short gap between the pole-tip and soft under layer. The recording layer that stores the data is directly in this gap where the field is most intense. Higher fields allow ‘higher coercion’ media to be used. Such media require higher fields to set the magnetization is inherently more stable.
The presence of the soft under layer also strengths the read back signals and helps decrease interference from adjacent tracks

4)Read Element:
The read element is basically made up of a “giant magneto resistive” device known as the GMR. Basically this device measure small changes in magnetic field. As the magnetic bits on the hard drive pass under the head, the current decreases due to resistance and theses changes in the current are measured to figure out what the bit contained.
This is how data is basically read off the hard drive.

5)Shield:
The shield helps in keeping the magnetic field from affecting stray parts of the head. This ensures that the neighboring magnets do not lose their orientation thus preventing loss of data due to loss of magnetic orientation.