Loosely Coupled & Closely Coupled multiprocessor configuration

Loosely Coupled Multiprocessor: Loosely coupled multiprocessor system is an alternative model of microprocessor. In this type of system, each processor element has its own private local memory. A switching mechanism constructed to transmit information from one processor to another through a message passing scheme used to couple the processors. The  processors relay data and program to other processors in packets. A packets includes an address, the data content, and some error detection code. The packets are addressed to a particular processor or taken by first available processor, based on the communication system used. Loosely coupled systems are most efficient when there is minimal interaction between the tasks.

Closely Coupled Multiprocessor: tightly coupled system is defined as a multiprocessor system with common shared memory. This allows each processor of having its own local memory. Usually, a cache memory with each CPU is provided by most commercial closely coupled multiprocessors. In addition, there is a global common memory that all CPUs can access. Thus, common global memory is responsible for sharing the information among the CPUs. This system can tolerate a higher degree of interaction between tasks.