In Pictures: Most excellent tech toys from the '90...
These secondary cases were used in some early CD-ROM drives to make sure the disc didn't get scratched, or something. To be honest, we're really not sure what the point of them was. We remember them always getting stuck and causing us to blow our stacks out of frustration.
Credit: OldSoftware.com/God, we hate CD caddies
In Pictures: Most excellent tech toys from the '90s