Little tip for Mac users who take their laptops out with them while forgetting there's still an optical disc spinning and vibrating in a drive that they don't have a case for, there are two quick things you can do!
Tip the First: simply fire up a Terminal and enter:
# umount [-f] [volume name]
Tip the Second: go to Applications > Utilities > Disk Utility.app, select the optical drive and click Unmount. In either case, the optical disc will stop spinning which will make your laptop quieter and save battery life, but it's still protected from not being taken out of the drive without a case.
Just like that Mercedes Benz radio advertisement in Singapore, it's not that we don't know these things, it's just sometimes we need a little reminder :).