Abstract: A multi-nodal data processing system in which each node has a local memory for storing message send vectors, one for each other node in the system. When a node has a message to send, it places the message in the message send vector corresponding to the destination node of that message. When a node is ready to receive messages, it reads messages from the message send vectors corresponding to this node in the other nodes. Each message send vector has a head pointer and a tail pointer for defining the head and tail of a queue of messages. Each tail pointer is held locally, in the same node as the message send vector to which it relates, while the head pointer is held in the destination node of that message send vector.