Tightly Coupled MIMD Architecture : Shared Memory

A multiprocessor system makes use of more than one CPU along with memory and IO channels. They are capable of processing multiple instruction, multiple data (MIMD) programming. Thus, they support concurrent operations. The configuration of processors in a multiprocessor system can be loosely coupled or tightly coupled. The major distinction between these two types of multiprocessors is the way memory is organized. Tightly coupled systems share a single memory space and share information through the shared common memory.

Tightly coupled Multiprocessor is a multiprocessor system in which the processors communicate with each other through shared memory, in contrast to a loosely-coupled multiprocessor system in which processors communicate over a network. In Tightly coupled multiprocessor the degree of coupling between processors coupled system is high. The Tightly coupled multiprocessor has shared memory modules. It is Efficient for high-speed or real-time processing, but it experiences more memory conflicts in comparison to loosely coupled multiprocessor. The Tightly coupled multiprocessor is more more expensive then loosely coupled multiprocessor.

The tightly coupled system has processors, shared memory modules, input-output channels. The above units of the tightly coupled system are connected through the set of three interconnection networks, processor-memory interconnection network (PMIN), I/O-processor interconnection network (IOPIN) and the interrupt-signal interconnection network (ISIN). The use of these three interconnection networks is as follow :

PMIN : It is a switch which connects each processor to every memory module. It can also be designed in a way that a processor can broadcast data to one or more memory module.

ISIN : It allows each processor to direct an interrupt to any other processor.

IOPIN : It allows a processor to communicate with an I/O channel which is connected to input-output devices.

The tightly coupled system has shared memory which increases the data rate.

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