Hard Disk Recording Technology

Over the last few years with magnetic recording densities fast approaching the limits of areal density and the rapid increase in SSD capacities, the days of the hard disk drive have come into question. Prices and further advances in technology are however ensuring that hard disk drives will remain the most common mass storage media for many years to come.

In spite of the continual research and development being undertaken by hard disk drive manufacturers, the techniques used in the data recovery process are relatively unchanged. This is in contrast to SSD technology where the rapid development of proprietary technology makes data recovery a moving target, requiring new techniques to be developed.

Perpendicular Magnetic Recording

The first major advance allowing a significant increase in drive capacities was the development of the perpendicular magnetic recording method (PMR). The alignment of the data using this technique is alignment perpendicular to the surface of the platter, rather than the traditional horizontal method, which allowed the recording density to be increased by several orders of magnitude.

The addition of a heating element to the read/write head, along with separate a read and write head, allows the magnetic field to be focussed, which also allowed a further increase in density. This technology is however reaching a physical limit.

Shingled Recording Method

One method to overcome the problem of the limit in density has been the development of the shingled recording method, whereby the data is overlapped. This however comes at a cost to write speed, as all data in a 4kB sector must be rewritten when any changes are necessary. These drives are therefore marketed for archive purposes and not recommended for general everyday use.

Layered Recorded Method

A paper has recently been released detailing a proposed method of recording separate layers with the magnetic medium, which would allow a significant increase in recording density. The ability to access data on the separate layers is realised by using different microwave magnetic frequencies. This represents the next biggest step in hard disk capacity which can be manufactured, while providing the best performance available from the technology.

Other Techniques to Increase Capacity

Flutter from spinning platters imposes another limitation, this time on the number of platters which can be used and their thickness. One method which allows for thinner platters without increasing the flutter to the point where the read/write heads impact with the surface is to fill the drive with helium. The use of an inert gas allows thinner platters to be used while allowing the maximum number possible in the form factor.

A proposal to also go back to using the 5.25” form factor is under review, which may also allow a further increase in capacity. The future for the hard disk drive appears to have many years, especially as SSD’s are so much expensive per GB. Data recovery from traditional hard disk drives is easier than SSD’s with a much higher rate of success.

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