Cerebro is a powerful supercomputer that the X-Men (in particular, their leader, Professor Charles Xavier) use to detect humans, most specifically mutants. It was created by Xavier. Cerebro also amplified Professor Xavier's telepathic abilities, enabling him to home in on the X-Gene and finding mutants.
Cerebro was first used by Xavier in 1987 and detected Kal-El's arrival to Earth. Xavier was strained from using Cerebro and passed out for three hours. Years later, Cerebro again detected Kal-El's power signatures in the Fortress of Solitude in which it brought Xavier and the X-Men of their first encounter with Superman.
Cerebro's computing power was briefly boosted with one of the Fortress of Solitude's crystal-processors by Superman to find a Kryptonian Speeder, but failed in finding it. Although, Cerebro did managed to get a glimpse of Earth's entire mutant population.