When several computers need to work together, as when calculating in parallel on several parts of a single large problem or managing a large database, they need to keep in step. These situations are particularly common in large data centers that make up “the cloud” where institutions farm out their computing needs. So a Cornell computer scientist has come up with a new system, “Datacenter Time Protocol” (DTP), in which signals sent at the speed of light over fiber-optic cables between the computers enable them to stay in sync to within a few nanoseconds.