Holographic disks

...holographic discs, with the technology G.E. has attained, could hold 500 gigabytes of data. Blu-ray is available in 25-gigabyte and 50-gigabyte discs, and a standard DVD holds 5 gigabytes.

"We have books here bound in the hides of echidnes, krakens, and beasts so long extinct that those whose studies they are, are for the most part of the opinion that no trace of them survives unfossilized. We have books bound wholly in metals of unknown alloy, and books whose bindings are covered with thickset gems. We have books cased in perfumed woods shipped across inconceivable gulf between creations--books doubly precious because no one on Urth can read them.

"We have books whose papers are matted of plants from which spring curious alkaloids, so that the reader, in turning their pages, is taken unaware by bizarre fantasies and chimeric dreams. Books whose pages are not paper at all, but delicate wafers of white jade, ivory, and shell; books too whose leaves are the desiccated leaves of unknown plants. Books we have also that are not books at all to the eye: scrolls and tablets and recordings on a hundred different substances.

"There is a cube of crystal here--though I can no longer tell you where--no larger than the ball of your thumb that contains more books than the library itself does. Though a harlot might dangle it from one ear for an ornament, there are not volumes enough in the world to counterweight the other."

- Master Ulton, the Curator, from Gene Wolfe’s "The Shadow of the Torturer."