AFAIK, that's only true if your running a decent ide cable, such as an 80 pin or a more modern version of the 40 pin, and install the old hard drive on the middle connector. In that configuration, it will default to cable select, and since the middle connector is the "slave" connector, the old hard disk is automatically slaved. Also, your trick will not work on other brands and models of hard disks where the lack of jumper actually defaults the hard disk to Master/Single. Also, unless you've been working on computers from before 1995, there is no need to go into the bios once you've slaved the jumper on a hard drive.
Face it, you got lucky. What you did is not correct; it just happend to work for you. If you care to disagree, please point me to online information where it is a universal rule that un-jumpering a hard disk turns it into a storage drive. lol, even the term "storage drive" would imply that it is not the operating system drive, and as such would then have no other choice but to be the slave drive, you hoser. :lol: