Perpendicular Recording

Perpendicular recording can increase magnetic media's capacity as much as 10 times. That means that microdrives that used to hold about 3,000 songs could provide room for about 30,000 songs. In more technical terms, that means it will be possible to store about 230 gigabits per square inch, or up to 20GB, on a 1-in. microdrive.

It's the Moore's Law type of advance that disk drive manufacturers had begun to fear was becoming unattainable. From the advent of hard disk drives in 1956 with IBM's RAMAC drive to the present, disk drive capacities have increased almost exponentially. Capacities almost doubled annually for the first decade or so after RAMAC, slowing their increase a bit for the next 20 years but then picking up the pace again in the '90s. From RAMAC's 1,800 bits per square inch, they reached to about 100 gigibits per square inch, and this increase occurred while the platters shrank from 24 in. to 2 in. and 3 in.

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The increased capacity and miniaturization allowed for a host of new applications -- high-quality video and audio in portable containers, as well as laptops that allowed people to work for extended periods.

But for a while, it looked as if disk drive technology was reaching a hard ceiling at about 100 gigabits per square inch.

In horizontal or longitudinal recording, magnetized regions representing bits are laid out end-to-end like dominoes flat on a table. They are organized in concentric circles around the hard disk.

Read and write heads fly a few nanometers above the surface and the flat magnetized regions. If the magnetization is in one direction, that would signify a digital one. If it is in the other direction, that would signify a digital zero.

The strength of the magnetized area has to be great enough so that the head could sense it and the signal processing software in the disk package could determine the direction of the magnetization.

If the strength of the magnetization were to fall below some threshold, the head would not be able to sense it, and/or the signal processing software would not be able to figure out whether the bit was a one or a zero.

The sizes involved in this longitudinal arrangement were progressively shrunk to realize greater bit density. The size of each magnetized area was shrunk down to about the smallest size feasible.

Each magnetized area is composed of tiny magnetic regions called grains. When all the grains line up in one direction, the magnetization of the whole region is strong in that direction. If some of the grains flip their polarity, the magnetization of the whole region is weakened, and a hard-drive read head may have more difficulty reading it. If all the grains, or some large number of them, were to flip, the polarity would be reversed.

It takes about 100 grains to make a magnetized region reliable for recording digital ones and zeroes. Fewer than that, and a drive becomes prone to errors.

At small-enough sizes of magnetic regions and magnetic grains, the ambient heat energy in the hard drive can be enough to make a grain flip its polarity. This is called the superparamagnetic effect, and it limits how small magnetic recording media can be. But with perpendicular recording, manufacturers have been able to lift the ceiling and squeeze more bits into hard-disk real estate.

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