We’re all excited to get new technology — but what do we do with the old stuff?

One of the common questions I get is “what should I do about my old computer?” There are several options, but the first step before selling it, donating it, or recycling it is to securely erase it. I’ll outline a few techniques in this article for some of the common equipment you might want to discard.

Background

Computers and electronics with traditional hard drives take a long time to properly erase. When you delete a file, the file isn’t deleted — it’s just marked as free space and available to be written over. It’s important that you erase this available space, otherwise someone may be able to come behind you and recover all those files you thought were gone. To properly do this, you’ll want to write fresh data across the entire drive, ideally more than once.

Newer flash-based computers are a little more complicated to erase because of the wear leveling technologies they use. To help make sure flash-based drives get properly erased, it’s best to encrypt them with technologies like Bitlocker (Windows) or FileVault (Mac) before you erase them.

Macs

To securely erase a Mac, you’ll want to use the Disk Utility. Modern Macs can be booted from the internet using recovery mode (Option – Command – R loads the most recent OS the computer can run). Once in the recovery mode, you can run the Disk Utility to fully erase the built-in hard drive. Make sure to select the option for a multi-pass secure erase – it should take hours to complete.

For an older Mac that doesn’t support internet recovery, a boot CD or bootable firewire hard drive can be used to boot the computer and launch the Disk Utility to erase the built-in drive like you would from Internet Recovery.

Newer Macs use flash-based memory, so you’ll want to be sure to encrypt these machines with FileVault. Once encrypted, boot them up in recovery mode, erase the drive and reinstall a clean operating system. You won’t be able to select a secure erase option for a flash-based Mac, but you can overwrite the data from the Terminal if you want some extra assurance after doing a quick erase of an encrypted drive.

Windows PCs

I’ve historically used DBAN to erase older Windows PCs, but it’s not as reliable on newer systems. Another handy tool is the GPARTED live CD (or bootable USB). Once booted, run the command:

hdparm --security-erase NULL /dev/x

where ‘x’ is the device you are trying to erase.

On newer PC’s with flash memory, be sure to encrypt the drive with Bitlocker before erasing it.

Yeah, but old computer won’t even turn on!

There are other options if you can’t get the computer to power on at all. Removing the hard drive so you can erase it in another computer is generally a pretty good option, but some computers are easier to take apart than others. In general, the easiest to remove will be a Windows desktop PC, and the hardest will be a Mac laptop. Once you get the drive out, you can also physically destroy the platters inside it to be sure nobody gets to your data.