Paul deVries
Perpendicular Bit Recording
The Problem: Current hard drive technology uses Longitudinal Bit Recording (LBR) and the limits of this technology are taking affect. Individual bits on a hard drive are getting so small that if they decrease in size any more then an effect called superparamagnatism. This phenomenon is where the magnetic field in a bit becomes weak enough, because the bits are small enough, that thermal energy can randomly flip polarities or demagnetize a bit causing the data held there to become corrupt. The limits of LBR are believed to be around 150 gigabits per square inch. That means that a hard drive using LBR technology could be as big as 450 Gb for a single 3.5” hard drive.
The Solution: The best solution, at this time, around this problem is to use Perpendicular Bit Recording (PBR) instead of LBR. In PBR bits are aligned perpendicular to the hard drive platter instead of parallel to the platter, as in LBR. This can be seen in the figures below:
Longitudinal Bit Recording (LBR)
http://www.bellmicro.com/partners/linecard/suppliers/hitachi-global/PMR_white_paper_final.pdf
Perpendicular Bit Recording (PBR)
http://www.bellmicro.com/partners/linecard/suppliers/hitachi-global/PMR_white_paper_final.pdf
In addition to aligning bits perpendicular to the platter, PBR introduces many new problems. A soft under layer had to be made to put the bits into so they didn’t just fall apart, a new read/write head had to be developed and new signal processing had to be implemented in hardware to figure out what the read/write head was processing. These are just some of the problems faced with PBR. The good news is that hard drive manufacturers have already dealt with these problems when using LBR. Nothing drastically new had to be invented to switch from LBR to PBR.
The Benefits: Switching to PBR is expected to increase the capacity of hard drives about ten fold. That means when PBR reaches its limits with respect to superparamagnatism a single hard drive could possible hold 4 Tb of data. It also increases the transfer rate since more data can be read in a given second.
The Manufacturers: Out of the five major manufacturers only a select few have made the move to put their full production power into PBR hard drives. Here is a list of each company and their top model for each form factor, 3.5”, 2.5”, 1.8”.
|
|
Seagate |
Samsung |
Toshiba |
Fujitso |
|
1 Tb 3.5” |
300 Gb 3.5” 15k RPM |
No 3.5” Model |
No 3.5” Model |
No 3.5” Model |
|
200 Gb 2.5” |
160 Gb 2.5” |
160 Gb 2.5” |
No 2.5” Model |
No 2.5” Model |
|
No 1.8” Model |
No 1.8” Model |
No 1.8” Model |
40 Gb 1.8” |
No 1.8” Model |
It should be noted that Seagate’s 3.5” hard drive is specifically designed for use in servers where a high transfer rate is needed. Seagate’s model is estimated at 125MB/s.
Conclusion: As
hard drive manufacturers are switching to this new technology they are already
looking to the future for completely new designs. PBR is not going to give much more than ten
years of life into the hard drive industry.
This doesn’t mean that switching to PBR is bad. Instead it is allowing researches time to
develop innovative solutions to the increase demand for storage.
Sources:
http://www.anandtech.com/storage/showdoc.aspx?i=2474
http://www.seagate.com/docs/pdf/marketing/Article_Perpendicular_Recording.pdf
http://www.xbitlabs.com/news/storage/display/20060418031546.html
http://findarticles.com/p/articles/mi_m0BRZ/is_5_23/ai_103731260/pg_1
http://www.bellmicro.com/partners/linecard/suppliers/hitachi-global/PMR_white_paper_final.pdf
http://www.hitachigst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html
http://en.wikipedia.org/wiki/Perpendicular_recording