Never, ever, dispose of your harddrives without first erasing all the data in them. Also, make sure you don't erase it just by deleting the files; even after you delete files, they can be recovered. Your best bet is to properly overwrite the harddrive with bogus data, then erase it.
This process ensures that your data was erased, not by deletion, but by being overwritten which makes it extremely hard to recover and most of the times its impossible.
Sometimes the harddrive you're going to get rid of is actually broken, it won't spin, it won't power on or it clicks but it doesn't show up in your computer. Don't just throw it out! Even if you can't get it to start up, somebody else might be able to. Then they could have your data. The best way to make sure that your data is completely unrecoverable if the disk doesn't even turn on, is to drill through the drive.
- Get a drill
- Get your HardDrive
- Need a surface like a workbench
- A Vise would be ideal
- Drill a couple of holes through the platters of your disk.
- Dispose of the drive properly; electronics need to be recycled, don't just dump them in the trash.
Not sure what I mean by drilling out your harddrive? take a look at this video where we destroyed one of these drives that wouldn't turn on at all.
Take a look at this guide to help you wipe a hard drive clean if you're doing it from Linux. How to wipe a hard drive clean in Linux.
Safer than anything would be to first wipe the drive, like the instructions say then to destroy it physically like the video shows. Good luck!