How to factory reset a Mac?

Hey there. It’s been a minute since I messed around with this kind of stuff. I remember back in the day with old spinning hard drives, if you were constantly writing and deleting files, everything would get fragmented all over the place, which really slowed things down. Back then, there was this way to run a defrag—basically just tidying everything up without actually deleting your data—to get everything lined up again. How do I go about doing something similar on an Apple computer today?

Formatting usually means wiping everything out.

You’re probably thinking of defragmenting instead.

http://www.macworld.co.uk/how-to/mac...p-mac-3600241/