Heroic: Archivum Data Disc and its Normal mode equivalent: start the quest chain required for access to Algalon the Observer. It follows the vein of the Malygos attunement, where only one player in the raid needs the key to gain access to the boss.
This platinum disc is surprisingly symmetrical and devoid of any scratches or imperfections. Engraved along it's edge, bold runes spell out the word "ARCHIVUM."
There must be a device inside Ulduar capable of reading the disc.