In my former life, I was a computer expert who in addition to working for companies like Microsoft and UBS Swiss Bank, was also a court-appointed computer expert.  The following post from Point of Law reminded me of my former career:

Throwing out an obsolete PC

It can prove a costly mistake if it contains information arguably relevant to a legal dispute you're in...

Source: PointofLaw.com | PointOfLaw Forum: Throwing out an obsolete PC

If you want to get rid of an old PC, but don't want to lose the data, simply remove the hard drive and keep it on a shelf.  All the data you're obligated to preserve will be on that drive, and the drive will be the size of a paperback book, if not smaller.

If you want to destroy the data, yank the drive and drill a hole through it with a big drill bit.  Perhaps the CIA could recover data from the drive, but your average civil litigants will lack the means.

And if you want to surreptitiously destroy the data, put the biggest magnet you can find on the drive and leave it there for as long as you can.  Back in the day, you used to be able to buy VHS tape erasers from Radio Shack.  Due to the waning popularity of VHS, I don't think you can find them anymore, but they will do the trick if you can find one.

Oh - no matter if you're the plaintiff or the defendant, make sure to comply with all applicable discovery orders.  Spoliation isn't nice.