Originating Author: Fred Moore
Since the early 1990s, disk areal density has increased an average of 60 percent annually. This decade-long trend is just beginning to slow as the first signs of the super-paramagnetic effect are appearing. Manufacturers are enhancing disk read-write heads and recording media to help push areal densities higher. A new recording technique is evolving called vertical or perpendicular recording with areal densities initially ranging somewhere between 100 and 150 gigabits per square inch. The magnetization of the bits stands them on end perpendicular to the plane of the disk and, therefore, the name vertical recording. The rate of disk areal density improvement is expected to remain at the 40 percent level for a period of time due to the remaining unknown issues in making the future recording technologies work with the oncoming super-paramagnetic limit.
Disk form factors have fallen below a 1.0-inch diameter with the 0.85-inch currently the smallest. Data center disks use the 2.5- and 3.5-inch diameter disks while personal appliances currently use the sub 2.5-inch drives. Future seek time reductions are expected to be minimal as most of the performance improvements that lie ahead for disk drives will come through faster rpm, possibly as high as 20,000 rpm, yielding higher data transfer rates. The shift to 2.5-inch drives is under way.
A looming challenge will be to make magnetic recording heads with track-width dimensions that are smaller than the minimum feature size of the optical lithographic equipment used in the semiconductor industry. Thermo-mechanical data writing on a variety of hybrid substrates has shown initial positive results and may eliminate the long-anticipated super-paramagnetic limit completely. Nonetheless, the march to terabyte and higher capacities is now under way and the steps needed to get there have been identified if not yet completely resolved. Disk technology roadmaps indicate that disk drive capacity will approach 5 terabytes by 2015 even accounting for the challenges ahead.