16th July 2006 - 04:53 AM
This is the 2nd note I've seen about hard drive magnets. Since no one else is going to answer, I, the person who knows NOTHING about hard drive magnets will.
Here's a link: http://www.7volts.com/magnets.htm
This explains what they are, how to get them out, and how to draw blood by getting your fingers pinched between them. It appears you can get 4 of them out of an old hard drive, and the older the drive, the more magnets or bigger magnets you get.
According to the article, these magnets are so strong that if you stick one on your fridge, you will break a nail trying to get it off. They are the strongest magnets you can find, because the more powerful the magnet, the faster your hard drive spins.
To answer your teacher's question:
The magnets are used in the mechanism that positions the heads. The magnets provide a strong magnetic field. Within the magnetic field is a coil. In order to position the heads, a current is passed through the coil generating a magnetic field within the coil. The interaction of this magnetic field with the permanent magnetic field generates the force that moves the heads. By varying the current in the coil, the heads can be precisely placed on the disc. In order to move the head mechanism very quickly from track to track, a very powerful magnetic field is required. If the magnetic field is weaker, there's less force moving the heads and the drive access time will be slower. Since drive manufacturers strive for the fastest access times, they must use the most powerful magnets they can find. Drive manufacturers have made great strides in making the read write heads and mechanisms much smaller and lighter. This means the later drives need much smaller magnets but they still need to be very strong or access times will suffer. The scientific reader will probably wonder why electromagnets aren't used instead of permanent magnets for the magnetic field. The answer is probably that heat production and power consumption would be dramatically higher with electromagnet use. Still, it was a good thought and I'm glad you thought of it.
These magnets are a little different from what would be expected. They're actually polarized with the poles on the flat surfaces of the magnets rather than at the ends. Most magnets will be "N" at one end and "S" at the other. These will have "N" on one flat surface and "S" on the other.
Hope that helps, and no, I can't answer any magnet questions.