I hope this is not too silly of a question but I feel like I am confused about this topic of demagnetization of CD's, DVD's, and external hard drives. Recently I have bought two identical external hard drives and I am planning to store them one on top of another in a relatively small container. I am curious, since they are not plugged into any power source when they are stored, could any problems arise later, such as demagnetization?

Does demagnetization occur with external hard drives like with CD's and DVD's? I heard CD's and DVD's need to be stored vertically to prevent demagnetization? Is this true? After how long do CD's, DVD's, and external hard drive start to demagnetize if they are not used?

1 Answer 1


Hard disks are commonly installed in PCs with very little separation. So stacking them even turned on is not an issue.

Note that inside a hard disk are multiple platters with multiple magnetic heads reading and writing data. If there was the potential for the magnetic influence to reach beyond the case of a hard disk into another hard disk, it would also influence the other platters inside the hard disk. So they simply wouldn't work.

CDs and DVDs are plastic, and writable ones use dyes to encode data. So there is nothing magnetic to demagnetise. You may hear from audiophiles that demagnetising CDs is important for sound quality. As is often the case with these things, it is nonsense.

  • CD's and DVD's need to be stored vertically to prevent demagnetization? Is this true? Not only is it not true, it's not even wrong. Dec 19, 2014 at 4:44

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