help...what causes hard drive failure ...2nd imac 2 -3 years old with bad hard drives

Well, platter drives can fail from a variety of reasons. They can have bad sectors (areas on the spinning plates) that become demagnetized, they can suffer from fragmentation (lack of manitence on users part) and or the read write head becomes damaged.... lots of other reasons.

2-3 years is average for HDD replacement. I know I just replaced my HDD in my laptop. It was 3 years old.

I have my own theory on this but I believe the quality of the drives has been, somewhat, sacrificed.

You have to do your homework when it comes to hard drives to see reviews and opinions of other computer users who can tell you which manufacturers and hard drive models are the most reliable.

Also, if you have one of the newer designed iMacs, say from 2008 forward, excessive internal heat from inside the iMac enclosure can cause premature component and hard drive failures.

Heat is the enemy of sensitive computer electronics and components.

I fully believe the newer iMacs are not sufficiently ventilated and are inefficient at expelling enough of the iMac's internal heat.

The result is that, basically, you are slow-roasting the iMac's internal components to failure over time.

Apple designers and engineers are more concerned about design aesthetics and quiet operation than how long components in these new iMac designs will last in an over heated internal, enclosed environment.

Apple is designing their consumer iMac design to be a disposable product in 5 years or earlier depending on a major component failure, like the CPU or complete logic board.

I, personally, can't afford to buy a new Mac every couple years or 5 years. Apple can keep making new product, but they should make a product that will still function well for years past whatever artificial obsolescence date they put in their older products.

I bought my 2009, 27 inch screen iMac used. I don't know how it's previous owner treated this iMac, but I have taken precautions and actions to keep the inside of my iMac as cool as possible.

I want to have this Mac run trouble free for another 4 or 5 years.

My previous PowerMac ran for almost 10 years without any hardware failures because it was well ventilated and stayed cool.

Anyhoo, this is my take on why hard drives and component failures happen in the current iMac designs.

Someone will, undoubtedly, argue and disagree with my points here, but this is my story and I'm sticking to it!!

I forgot to add that my statements made hard drive can and do fail prematurely from time to time.

Even when taking exceptional precautions.

The saying goes that for hard drive failure it's not a matter of if a hard drive fails, it's when will it fail.

Yeah,

You make some other good points, as well!

Still, excessive heat can make all of the hd components fail at once.

Well, I got some news.

I have a older external Western Digital hard drive that is going on seven years old.

I have an older external LaCie drive that's approaching 4 years old.

They have been well cared for and maintained.

And yes, if you do not do any regular drive maintenance, this can shorten the life of a drive, too!