During the Dark Times, Islos was home to a small settlement. The Tenth Doctor left Wim and Peschell on Islos after the Kotturuh destroyed Magnox. Over the years many survivors of Magnox came to Islos and founded a new centre of knowledge there, with Peschell as the Oracle.
Thirty years later, the Eleventh Doctor visited Peschell and chatted with her, pretending to merely be a friend who had come to apologise for the Doctor's actions. By this point there were about three-hundred Magnoxians living on Islos. He gave her a data drive he had recovered from the ruins of Magnox for their library. The drive contained the whole history of the Magnoxian society and three percent of all knowledge from the Dark Times, which the Doctor estimated could expand their library over a thousand fold. Before he left Islos aboard his TARDIS, Peschell realised he was the Doctor and thanked him. (AUDIO: The Minds of Magnox)
Islos became home to the Archive of Islos and was defended by orbiting weapons platforms. Islos was attacked by the Dalek fleet, led by the Emperor of the Restoration, as they were aiming to gain access to the Archive. The Daleks managed to break through the defence line of weapons platforms and cause large damage to the planet, but the Archivians surrendered the Archive only when the Emperor threatened to destroy it. The population of the planet escaped through a portal inside the Archive, taking its contents with them. In exchange, they offered the Daleks to an entity that saved them. (WC: The Archive of Islos) After the Daleks realised that it was a trap, they retreated from the planet and headed for Skaro. (WC: The Sentinel of the Fifth Galaxy)