What protection does MYST 3 use?

[Caslon]

I was too chicken to actually uninstall all the way. The backup install #1 disk started to unistall the game and removed the main dir. Luckily...the backup 1,2,3,4 disks
reinstalled ( I saved my savedgame files).
I used the real Disk1 to finish out the
reinstall. I don't know why I did that.
I had sixth sence if I'd used the backup #1 to complete reinstall, it would not have worked.