Hacker News Reader

I think you should be careful about taking the notion of 'flying' the head too literally. Think of the air as a 'spring' which is holding the head at a precise distance above the platter, the head is pushing "down" and the spring is pushing "up", so if the head is too far away its down force is stronger and it moves closer, if the head is too close the air's "up" force is stronger so it moves away. This is simply a very precise way of placing the head over the platter, which is necessary because the shape of the magnetic field is a sphere and the 'circle' of its intersection with the platter is determined by the distance from the platter by the head.

In terms of the mystery thing 'x', most of what you might think of as candidate materials have been tried. The challenge is to reliably (well at least reasonably so) flip the state of a bit on the substrate in about a microsecond. And do that as cheaply as possible.

It is exceptionally challenging engineering.

Your description is a much more precise way of looking at it. I was trying to reach for the same concept when I talked about fluid dynamics and the forces acting on the head cancelling out so that it rests at exactly the right distance, but I lacked the clarity to state it so neatly. Thanks!

>>> It is exceptionally challenging engineering. <<<

It's also very beautiful... When you look at something like that it's a bit like looking at a work of art - I don't know how to explain it but it is awe inspiring. I wonder how people end up working on such things... How do you get to the point where you can raise your sleeves and create a system as beautiful as this?

I don't think any one person can create a piece of engineering as complex as a modern day hard drive. There are just too many disciplines involved: Physical, electrical and embedded software engineering, applied physics, information theory for encoding the data and recovering from errors. But certainly a single person or group in those fields can be responsible for specific breakthroughs.

Re: the last part about etched semiconductors:

Keep in mind that the size of a magnetic grain (which stores 1 bit, roughly) is about 8nm. Compare that to the current cutting edge lithography scale of 14nm, which is the size of the semiconductor 'wires'.

Thus, a bit is smaller than the size even of the wires in any semiconductor circuit we can build, which means a system as you describe would have much lower storage density.

"Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and then use a linear actuator to move the reader back and forth - exactly like optical drives?"

The head is only "flying" relative to the platter. A hard drive works pretty much like you describe -- a short stack of fast-spinning platters and a read/write head on a swing arm that pivots back and forth over the platters.

A pic: http://msuweb.montclair.edu/~maciakl/blog/img/hd.jpg

They are child's play to take apart (http://turmon.org/Images/celeste-disk.jpg)

Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and then use a linear actuator to move the reader back and forth - exactly like optical drives?

The read/write arm needs speed and extremely fine-tuned movement that can't be had from a mechanical actuator. See: https://www.youtube.com/watch?v=Wiy_eHdj8kg