(Post 23/05/2006) Part 1 explained how perpendicular Recording can pack more data together. By having data recorded in two levels the data bits can be smaller and packed closer together. Just this step ensures that data can be packed more closely than thought with possible improvements of over 10 times being suggested by various research papers. The data tracks can be smaller, which increases density and the amount of surface affected is very clearly defined allowing associated bits of data to be more closely packed.

Another advantage here is that the media itself can be reassessed. In traditional media, there is no guarantee of how the particles are aligned on the surface of the media. This means that a proportion of the potential surface is lost. With PR, the direction of the particles is irrelevant as you are building up, not along. The result should be that the media is used much more effectively than at present.

The magnetic properties of the particles also work better for PR than for LR. Imagine a row of magnets on a table and you immediately need to deal with magnetic repulsion from the poles. LR suffers from this problem as bits try and flip the nearby opposing particles due to opposing poles. With PR the magnets lie alongside each other so there is reduced pressure at the poles and therefore much less likely to cause particles to flip.

One of the key advantages of the SUL in PR is that it allows for more thermally stable materials to be used. It also provides a write surface twice the thickness of LR. This means that the effects of the superparamagnetic limit are reduced allowing for higher densities before this problem is encountered. Yet the SUL may not be quite as perfect a solution as thought.

Researchers are already highlighting problems that need to be addressed with choosing the materials for the SUL. The magnetic moment, the thickness and the need to properly optimise the SUL material to the media all carry big problems that have taken time to overcome. They are especially difficult as we are not talking about slow, low run, hand-tooled solutions but high speed production line environments where media must be produced in significant quantities to be cost effective.

Eventually, even PR will have to accede to the demands of the superparamagnetic limit. At that moment in time, we can expect to see other technologies begin to emerge such as Heat Assisted Magnetic Recording (HAMR).

So where are we with Perpendicular Recording drives?

The first real hint of the success of PR was in 2000 when Hitachi Data Systems Inc announced that it had produced an areal density of 52.5 Gbits/inch2. This announcement, the first from a major drive vendor, meant that disks using PR could achieve the same storage capacity as disks based on LR. Since then, other disk vendors, notably Seagate, have driven that to over 100 Gbits/inch2. Dr Mark Kryder, Seagate senior VP of Research believes that PR could even drive storage to beyond 1 Tbit/inch2. This would mean that a single 3 inch disc could store over one terabyte (1TB) of data.

Seagate has announced that it expects to see PR drives within the next couple of years. It has already demonstrated the technology and now needs to see where it goes with solving the production issues. Since its announcement in 2000, where an overly optimistic press comment suggested drives in 2002, Hitachi has gone quiet on the subject of Perpendicular Recording.

Other vendors, such as Maxtor are currently concentrating on LR and how they can advance the current interfaces to provide better performance rather than becoming too focussed on a technology they are seemingly not convinced by.

With Seagate dominating the drive market, however, wherever they take the technology, others are sure to follow. For now, the other drive manufacturers seem to be content to let Seagate solve the problems of materials, heads, magnetic interference, manufacturing and the superparamagnetic limit.

Ian Murphy
(theo www.techworld.com)