If you use FileVault, any data "left behind" on your erased hard drive will be totally unreadable by your Mac's next owner. With a FileVault-encrypted startup disk, you can restart into OS X
How to Destroy a Hard Drive — The Family Handyman May 30, 2019 What to do before you sell, give away, or trade in your Create a backup. Make sure that you have a current backup of your important files. Learn how to … How to Safely Get Rid of an Old Computer - Techlicious Apr 13, 2020
What is the Hard Drive Cache and What Does It Do?
Nov 06, 2019
3 100% Effective Ways to Completely Erase a Hard Drive
May 14, 2020 How to "Completely Erase" a hard Drive - HP Support What you need to do is "wipe" the drive -- and this consists of overwriting the drive with ones, or zeroes, or both -- and that can take HOURS to do. IF you're prepared to spend that time, I recommend the use of a third-party tool known as Minitool Partition Wizard. This is a free partitioning tool and you should download their Boot CD ISO file How to Clean Up Your Hard Drive - Office Articles