Many sources quote Wikipedia which claims it is Spiradisk. But actually all sources refer to the Hackers book. And in that the text is vague but it's about Garriott arguing against Spiradisk and the guy who invented Spiradisk and responsible for the copy protection of Sierra games, giving in and implementing the copy protection after all (a bit vague but it's hinting that he implemented the old copy protection).
Also Wiki is not giving a source for the claim that the correct spelling is Spiradisc.Dick Sunderland called Duchaineau to tell him to copy-protect the old way. But Mark was still evasive. [..] Mark Duchaineau was in the awkward role of a hacker trying to stop another hacker’s worthy program from getting out. In any case, he agreed to copy-protect the product,