All the Weyrs of Pern1991

For generations, the dragonriders had dedicated their lives to fighting Thread, the dreaded spores that periodically rained from the sky to ravage the land. On the backs of their magnificent telepathic dragons they flow to flame the deadly stuff out of the air before it could reach the planet's surface. But the greatest dream of the dragonriders was to find a way to eradicate thread completely, so that never again would their beloved Pern be threatened with Now, for the first time, it looked as if that dread could come true. For when the people of Pern, led by Masterharper Robinton and F'lar and Lessa, Weyrleader and Weyrwoman of Benden Weyr, excavate the ancient remains of the planet's original settlement, they uncover the colonists' voice-activated artificial intelligence system—which still functions. And the computer has incredible news for them: There is a chance—a good chance—that they can, at long last, annihilate Thread once and for all. - from the cover