The IDE hard drive in a modern PC should be good for at least five years, and probably a lot longer if properly looked after. The mean time between failure for the average hard drive is currently about half a million hours of operation, or about 57 years.

I haven't seen a hard drive failure yet and I'd like to think that my appointment with the grim reaper of the storage world is still a fair way off. By "properly looked after", I mean that a disk should be regularly defragmented and checked for errors using a tool such as Windows' Scandisk. An increase in the number of bad sectors on a disk is usually a clear indication that the drive is getting close to failure.

When the day at last dawns and you get the message "No boot device detected" on startup, then, providing you've got a current backup of your data, you would expect that you could safely get rid of the drive.

But getting rid of a hard drive means different things to different people. My own method of disposing of a drive would probably involve a sledgehammer somewhere along the line.

If you're planning to upgrade to a bigger hard drive, reformatting the old one and putting it up for sale on eBay may be the worst thing you can do.

Your hard drive contains a rich stratum of data from your PC's working life and a format doesn't entirely remove all trace of what was stored on it.

And there are many unscrupulous people out there who would like nothing better than to mine what you thought was unrecoverable data on your old disk.

If you've been buying stuff online, even over secure connections, it may be that your credit card number is on the hard disk somewhere, along with corporate passwords and other interesting information, such as address books or sensitive documents.

Does your company have a policy for dealing with failed drives and for safely disposing of drives from expired desktops?

If you think this is just raving paranoia, then consider an IEEE study about data mining from second-hand computers by a couple of MIT researchers - see the web address below.

Entitled Remembrance of Data Passed: A Study of Disk Sanitisation Practices, it makes interesting and sometimes alarming reading for IT managers. The authors were able to retrieve thousands of credit card numbers from old systems.

In the US, the Supreme Court has ruled that legislation governing privacy does not extend to discarded items. So it appears that when your company disposes of its old computers in the US, it is giving away its rights over any of the data held on those computers.

So how do you sanitise your computer if you're selling it? The US Department of Defense lists three ways to do this: physically destroy the drive; degauss the drive to randomise the magnetic domains; or overwrite the entire disk area many times over with random data so that old information is obliterated. But if your paranoia knows no bounds, then there's always the oxyacetylene blowtorch option.

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