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So much for speed, what about storage capacity. Basically how much you can store on a drive depends on how tightly you can pack the data in.
This in turn depends on how smooth you can make the magnetic coating, how small you can make the read/write heads and how tight you can cram the tracks in.
As hard disks have developed recording densities have increased as better surface coatings, better heads and other breakthroughs have enabled the manufacturers to cram more bits per square inch.
The drive electronics has many other advanced features designed to make a drive more reliable and more efficient. For example, error detecting/correcting codes reduce the chance of losing data and cache buffers increase the speed of data transfer by reading data before your PC asks for it.
Ever since the first magnetic storage device was used in very early computers people have been predicting their end. Solid state devices such as RAM chips, Flash devices and variations on this basic idea have always seemed to offer a better alternative. As each new solid state or non-magnetic storage technology emerged from the lab the magnetic storage companies managed to find another level of performance that kept them in business.
Over the years hard disks have improved by the use of the same technologies driving the microchip industry. Read/Write heads were made smaller using microchip fabrication techniques and magnetic surface coatings were improved in the same way.
Now, just as the micro technologies look as if they are running out the disk drive manufacturers are turning to nano-technology and particle physics. Lasers are being used to create smaller and more accurate read/write heads. Quantum effects and spintronics are being used to create heads that are more sensitive and to create new materials for coating the disks. The most radical idea is to replace the magnetic read/write heads with tiny nano-mechanical stylus that can move individual atoms around!
It doesn’t seem time to count magnetic storage out just yet.