
These are disks on your Mac Catalina OS that you can “startup”, this is because they have operating systems on them.

Move files to an external hard drive or cloud storage.To make more space on your startup disk you will need to: So how do you fix your almost full startup disk? The same way you solve the problem of a packed fridge – you need to clear up space, of course.

What to do when your disk is almost full? If your startup disk is full and you get a message of warning from your Mac, this is a serious indication that you need to free up storage immediately.

A hard disk should never get beyond 85% capacity (especially a startup disk) as you will experience slowness and errors the further you get above that mark. It’s a lot like why is your fridge full? There is no more space! Your disk is almost full and this is very bad news for any drive. Why your disk is almost full on Catalina OS?
