A computer network is a group of connected computing devices that can send and receive data. Data travel in packets that carry a chunk of data plus metadata for routing and reassembly; packets may arrive in order, out of order or not at all. Having more than one path between devices gives redundancy, so the network can keep working when a part fails. Layers of software sit on the hardware to hide detail, and parallel computing can speed up a job, though the sequential part always limits the gain.