A new PMR technology for HDDs
A new PMR method of storing data on a hard disk drive (HDD) is the Two Dimensional Magnetic Recording (TDMR) technology. This method is currently being researched by Samsung and the company has stated that it will start introducing this technology in its HDDs by next year.
TDMR, which is based on the idea of Perpendicular Magnetic Recording (PMR), faces its biggest problem when the density of the tracks is very high, the track pitches are very small and the magnetic read heads are wider than the actual data track width. The data signals the read heads receives are getting worse since the data tracks are narrower and start to affect each other – an effect called Magnetic Inter-Track Interference (ITI). It becomes increasingly hard for HDD heads (readers) to perform read operations. Unfortunately, though the writing heads can be designed smaller, the read heads are unable to tackle this problem.
TDMR – as the name suggest – combines multiple read heads to read a single data track. Two Dimensional Magnetic Recording technology uses an array of heads to read data from one or several adjacent tracks. This enables HDD controllers to receive improved signal-to-noise ratio data streams and determine the correct data based on input from several locations.
Samsung states that using several read heads makes it possible to further increase the areal density by an additional 10% compared to SMR. By combining both the SMR and TDMR technologies, Seagate believes it can increase the areal density of HDD platters by about 10-20% versus today’s traditional PMR platters.
Other upcoming non-PMR technologies
To save even more data on a platter there are two other technologies currently being explored by manufacturers: HAMR (Heat Assisted Magnetic Recording) and BPMR (bit-patterned magnetic recording).
HAMR permits smaller bits to be written by using a diode laser integrated onto the magnetic recording head to heat up the disk where the data is about to be written. The laser is focused onto the disk using a near-field optical device. The small laser spot (in the order of tens of nanometers) heats the magnetic disk locally to make it easier to switch the magnetisation direction, which is how bits are written. The heat causes the magnetic grains to lose their superparamagnetic effect for a short period, allowing for smaller magnetic grains and higher areal density. When this small spot cools, the data is frozen in place and stabilised. The data is read in the same way as it is currently done. HAMR could increase areal density to 1.5Tbit/inch2, over 50% higher than today’s drives. Enterprise validation drives could go to market in 2017 and greater availability is estimated to be in 2018.
BPMR is the abbreviation for Bit-Patterned Media Recording and also tackles the density challenge. With this method, the grains sit on nanolithographically created, elevated “islands”. Without getting into much technical detail here, the aim is to make the grains smaller: one grain = one bit is achieved by putting a single magnetic grain onto each “island” of a bit-patterned medium and thus making the whole HDD platter even denser.
Although its inventor, Toshiba, is currently researching several aspects of the BPMR technology it is not likely to hit the market in the near future. If ever, it’s a technology that will become available in 10-15 years.
We are currently seeing several technologies developed side by side to get the most out of the magnetic hard disk drive. Some of the challenges for the technologies described here are far easier to tackle than others, and most likely every company is eager to get its products to market as fast as they can so their HDD business continues to perform while competing with SSD vendors.
Some technologies probably will last longer in the market than expected. For instance, SMR HDDs will not go away anytime soon since TDMR and HAMR are currently still not market-ready. It is more likely that those technologies will be mixed in the future as they become available: for example SMR or TDMR could be used in conjunction with HAMR. BPMR on the other hand, if it is introduced to the market, will be independently used as most of its problems and challenges are yet to be resolved.
One thing is certain though: with these technologies about to hit the market, the data recovery specialists will need to acquire the necessary knowledge to tackle the new challenges these technologies bring. Otherwise, they will be unable to physically recover data in an increasingly atomised environment.
Image source: Th. Reinhardt / pixelio.de