A parallel processor system has a plurality of nodes interconnected by a
network for communication under control of a network interface controller
of each node. The network interface controller includes a message
reception controller for receiving a message from another node and judging
illustratively the status of message reception and the need to return an
acknowledge message; an acknowledge generating unit for generating an
acknowledge message transmission request based on predetermined
information in the message and the reception status when the return of an
acknowledge message is judged to be necessary; and a message transmission
controller for receiving an acknowledge the message transmission request
and generating and returning an acknowledge message correspondingly. At
the receiving node, the network interface controller can return an
acknowledge message without processor intervention.