Stupid question on hard drives and magnets

[Loud_Silence]

I've been using computers for a long time now, but i still have a question kicking my brains.
Hard drives have magnets and coils inside, the magnets inside the spinning motor, and two very powerful magnets for the r/w arm.
If the hard drives are so sensitive that a small magnet outside can trash all the data stored on them, why the powerful magnets inside don't have any effect on the data?

[SUBMAN1]

Originally Posted by Loud_Silence

I've been using computers for a long time now, but i still have a question kicking my brains.
Hard drives have magnets and coils inside, the magnets inside the spinning motor, and two very powerful magnets for the r/w arm.
If the hard drives are so sensitive that a small magnet outside can trash all the data stored on them, why the powerful magnets inside don't have any effect on the data?

They are a constant. If you want to kill the data, you are going to need a strong electromagnet and you are going to need to move it all around the drive to pull the magnetic data out of position.

-S

[Loud_Silence]

I don't understand the constant part.

[Arclight]

The magnetic field caused by the parts doesn't change, ie it's constant.

If data is written while under the influence of this field, it will remain the way it's written since the field doesn't vary. By introducing another magnet, the field changes/is disturbed, and that's what influences the data layer, effectively altering/destroying the data contained on it.



Think of a compass: the Earth has a magnetic field, and the needle always points north because the field is constant. If you hold a magnet next to the compass, the needle changes orientation.

Think of the needle as the data: as long as it points north, it is correct, even though under the influence of a magnetic field (the internal HD parts). Changing the field (moving a magnet across the HD) puts the needle in an "incorrect" position (data is destroyed).