Message Passing Organization

• Message passing systems are a class of multiprocessors in which each processor has access to its own local memory.
• Unlike shared memory systems, communications in message passing systems are performed via send and receive operations.
• Nodes are typically able to store messages in buffers (temporary memory locations where messages wait until they can be sent or received), and perform send/receive operations at the same time as processing.
• The processing units of a message passing system may be connected in a variety of ways ranging from architecture-specific interconnection structures to geographically dispersed networks.

Two important design factors must be considered in designing interconnection networks for message passing systems. These are the link bandwidth and the network latency.

1. The link bandwidth is defined as the number of bits that can be transmitted per unit time (bits/s).
2. The network latency is defined as the time to complete a message transfer.