Loosely Coupled Multiprocessors

Introduction

Multiprocessors are classified by the way their memory is organized.

 

Multiprocessor system with common shared memory is classified as a distributed memory or loosely coupled multiprocessor.

Loosely Coupled Multiprocessors

In this system each processor has a set of input-output devices and a large local memory and input-output interfaces are together called computer module. Processes which execute on different computer modules communicate by exchanging messages through a Message Transfer System (MTS). Communication between tasks allocated to the same processor take place through the local memory. This coupling in such a system is very loose. Hence, this system is also called as distributed systems.  In diagram, module contains processor, local memory and I/O devices connected through Channel and Arbiter Switch (CAS). CAS consists of a high-speed communication memory which is used for buffering block transfer of message.

 

Figure : Loosely coupled multiprocessors system

The MTS are divided in to two categories: Simple time-shared bus, Shared memory system.

The time-shared bus is a common communication path connecting all functional units. On the other hand, shared memory system consists of a set of memory modules and a processor-memory interconnection network. The configuration of MTS is one of the most important factors that determines the performance of the multiprocessor system. However, communication between task allocated to different processors is through a communication port with in the communication memory. This system mostly used in distributed multiprocessor system.

Advantages:

Better system throughput

Parallel Processing

More flexible

More reliable

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