/don'gl disk/ (Or "key disk") A kind of dongle consisting of a special floppy disk that is required in order to perform some task. Some contain special coding that allows an application to identify it uniquely, others *are* special code that does something that normally-resident programs don't or can't.
For example, AT&T's "Unix PC" would only come up in root mode with a special boot disk.
Try this search on Wikipedia, OneLook, Google
Nearby terms: Donald Knuth « dongle « dongle cracker « dongle-disk » Don't do that then! » donuts » Dooced