Tech Primer

Perpendicular Magnetic Recording (PMR)

What is PMR?

Perpendicular Magnetic Recording (PMR) was first demonstrated in the 19th century by a Danish scientist called Valdemar Poulsen when he recorded sound magnetically. The hard drive industry was born in 1956 and since then horizontal recording technology has dominated hard drives. Later, in 1976, Professor Shun-ichi Iwasaki of Tohoku Institute of Technology demonstrated the advantages of perpendicular recording technology.

What is the difference between horizontal and perpendicular recording?

The difference between the two is in the way data is stored. In the conventional recording system the magnets representing the bits are lined up end-to-end along the circular tracks in the plane of disk. In such a scenario they repel each other, making them unstable against thermal fluctuations.

As the name suggests, in PMR, bits are stored vertically up and down in a disk. In this state, bits standing on the opposite poles, north to south pole, attract each other which increases their magnetic power. Due to the same reason they are able to stand more closely resulting in higher density of the disk in the same per square inch as compared to horizontal technology.

In horizontal recording technology, bits are stored end-to-end in the disk. Storing bits this way creates repelling magnetic effects as the adjacent bits are stored facing the same pole. This limits the data density to 150 gigabits per square inch. Exceeding this data density will result in the magnetic energy becoming equivalent to thermal energy, a state called supermagnetism.

Why do we need this technology?

With an increasing need for multimedia applications, there is pressure on the hard drive industry to enhance disk capacity. Following the trend of increasing capacity, we are expected to reach the saturation point within a few years. This is forcing the industry to look at technologies such as Media Recorders.

What are the benefits?

When the technology matures it is believed it will give a 10-fold boost to the highest storage capacity of horizontal recording technology. Analysts claim that the technology allows up to 250 gigabits to be crammed per square inch. The PMR configuration opens up a new avenue to continued capacity growth.

Which are the companies involved?

Major disk manufacturers include Hitachi, Seagate, Maxtor Corporation, and Komag.

For more details visit: www.komag.com/technology/perpendicular.html
www.hitachigst.com/hdd/research/recording_head/pr/PerpendicularPaper.html

—Sneha Khanna