Analysis

posted on 06 August 2008 12:59

---

Hitachi GST says it can produce a hard drive with 250 percent more data by 2010/11 through recording head, media and error code improvements. This is only half the capacity it was reportedly telling us it could achieve less than a month ago. 

Then it was reported as saying it could achieve a 5TB 3.5-inch hard drive by 2010 through use of Current-Perpendicular-to-Plane Giant Magneto-Resistive (CPP-GMR) heads, which were a follow-on from the current TMR (Tunnel Magneto-Resistive) heads. They couldn't deal with areal densities greater than c500Gbit/sq in. This represented a 3.3 to 4.4 times improvement on current areal densities of c250Gbit/sq.

Now it is telling us it can reach a 2.5 times density increase, to 610GBit/sq in, by using TMR heads and that it can deliver such disks, with 2.5TB capacity by 2010/11. What is going on?

According to a report featuring Hitachi GST quotes, the company can tune its TMR head technology and its recording medium along with error correction codes to incease TMR-based technology's areal density to a 635Gbit/sq in level.

The medium has narrower tracks and certain chracteristics are graded throughout its depth to improve its thermal stability and its recordability. The TMR heads use a so-called WAS (Wrap-Around Shield) structure to enable them to read the narrower tracks and not corrupt data on close-by adjacent tracks.

Lastly, LDPC (Low Density Parity Codes) provide a way of providing error correction and checking needing fewer bits than currently-used Reed-Solomon encoding. This enlarges the effective recording area by 4 percent.

Questioned about the timing of usable product an un-named Hitachi GST spoksperson said: "The surface recording density of our existing products is about 250Gbit/sq in. And it took us two to three years to develop this technology from the research and development stage. We aim to develop the 610Gbit/sq in technology in the same length of time."

That would give us 2.5TB product in the 2010-2011 period.

This, of course, directly conflicts with the early July reports saying Hitachi GST would each 5TB by 2010 through the use of CPP-GMR heads which overcame the obstacles met by shrinking TMR head technology.

The company has been asked if it can help clarify the two reports.

^{[Chris Mellor.]}