You don't want any personal information left on your Mac when you give it away or sell it. Do you take out the hard drive or SSD and smash it? Do you sweep it with a strong magnet? This guide provides effective and safe methods to wipe your hard drive or SSD.
Fewer people will be able to upgrade to this fall's macOS Mojave, which has tightened the minimum hardware requirements needed to install and run it, according to release notes from the developer beta.