Hard drive disk

What is the disk in a hard drive made of?

 

Will the magnetic layer eventually wear down or out and not record the way it did when new?

 

It's possible, but mechanical failure and circuit failure are all but guaranteed to take out a HD first.

Just like any magnetic or electrical storage, the state of the media degrades over time. That means that if you write to the disk and leave it for 50 years, it might not be readable anymore. This is not to say that if you read or write to a disk too much you will wear it out. The disk platters do not physically touch the read/write head (damage is caused if such a "head crash/slap" occurs). Magnetic media is simply subject to all the other electomagnetic fields that natually exist, and they eventually degrade the magnetic state.

I suppose it's also possible that the specialized treatments that the surfaces of hard drives undergo eventually wear out or cease to be effective. These treatments control the density of the data -- how close a 1 can be to a 0, and so forth. If those start to fail, you might not be able to read data.

It's not unheard of for drives to wear out, of course. They begin making mistakes on reading and so forth. Most modern hard drives use a technology called S.M.A.R.T. that monitors the drive and alerts you when it is beginning to fail. I guess I don't know if it's magnetic failure or circuitry failure or mechanical failure that causes this kind of degradation, but I suspect it is caused mostly by the electric motors wearing out and not rotating at the proper speed.