Invalid partition specified, or partition table wasn't reread after running fdisk, due to a modified partition being busy and in use. You may need to reboot to re-read your partition table. This prevented you from killing the system during such a dumb command. Later versions, resulted in the system halting with no activity. Again, a pretty good result for such a dumb command.
Memory is like gasoline.
You use it up when you are running. Unmounting and ejecting the root fs on shutdown.