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Hard Disk Drive
3.5inch vs 2.5inch
Longitudinal Magnetic
  Recording (LMR)
Perpendicular Magnetic
  Recording (PMR)
Insulated Gate Bipolar
  Transistor (IGBT)

Perpendicular Magnetic Recording (PMR)

Currently all magnetic media products are of the Perpendicular Magnetic Recording Media (PMR) type, which offers higher aerial densities with the same disk size. The maximum recording density of perpendicular magnetic disks is 5 times that of longitudinal ones based on comparison between the two of identical size of disks. The difference between PMR and LMR media is that the data (i.e. magnets) which is stored within the disks have a perpendicular orientation rather than longitudinal, i.e. in-plane orientation.

Longitudinal and perpendicular recording follow the same basic principle. As the write head passes by the disk surface, it leaves behind a magnetization pattern. For perpendicular recording, this magnetization pattern is ‘up’ and ‘down’ rather than ‘left’ and ‘right’ as for longitudinal recording.

This allows more data to be stored in one particular area. This means, if one bit can be stored within one area for longitudinal media, then by changing the orientation of the magnet on the media to perpendicular, the number of bits that can be stored in that area will increase. For example, if one room can fit 5 people who are lying next to each other, then that room can fit 25 people if they are standing.

A new feature in perpendicular recording media is the magnetically soft underlayer (SUL). The SUL belongs physically to the medium and magnetically to the head. There are changes from a recording system perspective in transition from LMR to PMR, because an efficient writing process requires the presence of SUL.

The future of HDDs depends on where the media and head industries are heading to. Medias will move on from PMR to Shingled Magnetic Recording (SMR), Head Assisted Magnetic Recording (HAMR) or Discrete Track Media (DTM). On the other hand, head devices will move on from Giant Magneto-resistive (GMR) head to Tunneling Magneto-resistive (TMR) head. This will in turn provide computer and electronics users to have larger data storage space over the next few decades, until either the technology itself becomes limited or the world comes to an end.


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