Getting rid of old drives...
Well... There's a LOT of different ways to do it. Some are more effective than others. Some are more permanent than others. It all depends on how far you're willing to go.
As you've no doubt heard, formatting a hard drive, removing the partition is pretty much useless these days. Formatting can be a "quick" or "thorough" format. A Quick format simply overwrites the part of the drive where the drive's index is stored - that's the part that tells the operating system where your files are physically located. A through format actually overwrites the entire drive - both the master file table (MFT - the previously mentioned index) and the data areas. A partition is a virtual container that defines how the data is stored on the drive. A partition is usually referred to in Windows by a drive letter.
The problem with the Quick format is that it only overwrites the MFT - leaving all the data intact. It's actually possible to undo a quick format and recover data fairly easily these days. A Thorough format is a bit better, but data recovery forensics these days can be likewise used to recover data.
So what can you do? There are a few options. There are programs (some freebies) that can format a hard drive in such a way that it makes it very difficult to recover data that's been wiped out. Many of these conform to Department of Defense (DOD) standards. The current standard for a DOD wipe is 5220.22-M. These programs accomplish a wipe by overwriting all of the tracks with random bits (ones and zeros) multiple times.
The only hitch with this - data recovery forensics have just about caught up with even a DOD level wipe. Of course, this sort of recovery isn't exactly common, nor is it cheap. Of course, that will change - like all things tech tend to do - it will get and more accessible.
Your best bet would be to do the DOD level wipe multiple times. Because the DOD wipe overwrites data multiple times, and if you repeat the process more than once, that means the data areas have been overwritten quite a few times. There's a limit as to how many changes (writes) the data patterns that were written on the hard drive can last under that sort of treatment and be recovered to their original content. It's doubtful that much, if anything would survive that kind of treatment. Perhaps in 10 - 20 years, someone might come up with a way to recover data that's been infintely overwritten.
The downsides to a DOD wipe - you have to install the drive on another channel AND it takes time. You wouldn't want to wipe the boot drive. It can take a fairly long time to completely process a drive multiple times - depending on how big the drive happens to be.
You can use Google to find these tools by searching for "DOD hard drive wipe".
Another alternative would be to use a heavy degaussing magnet, the kind used to bulk erase video tape (and other magnetic media). This can work, but it may or may not be quite as thorough as a DOD wipe. Under NO circumstances should your hard drive be plugged into a computer or any other power source while you're doing this if you go this route. Having a hard drive plugged into a power source while you're attempting to degauss it could damage the drive and anything else the tool might get close to.
If you wanted to put a drive permananetly out of it's misery, with next to no possibility of data recovery - the solution would be to destroy the drive. This can be done in numerous ways - drilling through the platter(s), a steam roller, a 50 ton press, dropping it off a cliff... You can get quite creative with that.
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