Photo: jon_a_ross via Flickr
Before passing on your old computer to persons unknown, you should make sure your data isn’t falling into the wrong hands.Both Windows and Mac OS X make it pretty easy to completely erase your hard drive and reinstall the operating system.
And if you want to keep your old system, it’s a great way to refresh your computer for future use.
Before you attempt and erase and install — and this should go without saying — make sure you back up all your important files. Otherwise, you’ll never see them again.
Open the Finder. Then go to Applications, Utilities, and open Disk Utility.
Click the Erase tab and select the hard drive you'd like to clear.
Click Security Options for a list of erase methods. We suggest selecting at least the Zero Out option because it will write over your data. The 7-Pass and 35-Pass Erase options take hours, possibly more than a day, but make it practically impossible for anyone to recover data from your hard drive. After choosing your option click Erase and let the Disk Utility do the rest.
If you want to erase your hard drive and reinstall OS X, you can run Disk Utility from the install DVD
Insert the install DVD. When the window pictured here appears restart your computer and hold down the C key until the computer boots directly from the disc. Select your language, then click the Utilities tab at the top of your screen and select Disk Utility. From there, run Disk Utility as normal. After the erase is complete, you'll be prompted to install OS X.
Just like Mac OS X, you can erase your hard drive on a PC with the built-in disk utility on Windows. The easiest way to do this is to boot your PC directly from the Windows 7 install DVD. Insert the install DVD and restart your computer. When prompted to do so, press any key to boot directly from the DVD.
You'll now have the option to format your hard drive and do a clean install of Windows. Follow all the prompts to install Windows until you are asked which kind of installation you want to perform. Select Custom (Advanced).
Now select the hard drive you want to reformat and install Windows to. This will erase your hard drive and install a clean version Windows 7 on your machine.
If you're still nervous about handing your hard drive over to a stranger, you can remove it from your old computer and destroy it. Go caveman-style and whack it with a hammer or crack the casing open and use a razor blade or key to scratch the disk. You can also hold a powerful magnet against it for several minutes, although that's not 100 per cent guaranteed to work. Either way, go green and find a recycling centre for your old hard drive when you're finished. Click here for the EPA's list of trusted recycling centres.