HDD Industry Trends - Part One: To the Present
This is the first in a two-part blog series that will explore HDD trends. We’ll get into what lies ahead in the next post, but first let’s look at HDD up to the present.
HDD will be here for years to come. Since 1997, the year in which giant magneto resistive (GMR) heads appeared, recording density improved by 100% annually until dropping to 30% in 2001, due to a slowing in the pace of advancement. The practical application of the perpendicular magnetic recording method restored the rate of improvement to 50% in 2005. In this way, technological innovations in magnetic heads and magnetic disks greatly contributed to improvements in recording density. However, channel technology, error correction technology, servo control technology, and other technologies have also facilitated improvements. Our current PMR (Perpendicular Magnetic Recording) process is nearing the end of its development, as any further decrease in the size of the magnetized bits renders them unstable, hence the need for storage firms to move on to newer, denser recording technology.
The unique attribute of the magnetic bit cell in a hard disk drive (HDD) is that the bits are unpatterned, offering a tremendous cost advantage in media manufacturing. The bit width is determined by the lithography used to form the write transducer, whereas the bit length is determined without lithography. It is defined by the distance the disk rotates during the time interval that alternating current pulses are applied to the write yoke. Unfortunately, newer HDD technologies are looking at creating new lithography processes. In fact, Patterned Media cells will require substantial “invention” in lithography to meet density goals. Bit Pattern Media (BPM) technology allows for small bit patterns to be physically processed and has also been studied as a magnetic disk technology. Toshiba has been developing these future technologies in collaboration with parts suppliers and its research and development divisions.
A temporary boost in HDD capacity is shingle writing or shingle magnetic recording (SMR), in which recording tracks partially overlap, increasing track density on a platter. This would be cheaper than a transition to BPM or HAMR and could extend the use of PMR technology for a couple of years, providing some financial breathing room. This technology uses existing perpendicular magnetic recording technology and improves recording density by altering the algorithm used to record data to magnetic disks. In this approach, data tracks are not separated when writing data, but a new data track is recorded while layering part of the data track over the previous track. Since this method of writing data resembles the way shingled roofs are installed, this technology is called shingled write recording. Although it depends on the limitations of the perpendicular magnetic recording device, a recording density of 1.5 to 2 Tbit/in2 can be achieved using this technology.
The next blog in this series will take us into the future of HDD, so be sure to come back in another couple of days.