Loosely And Tightly Coupled Systems

Loosely And Tightly Coupled Systems

Some, but not all, distributed systems are loosely coupled.

​Coupling refers to the degree to which two or more processes are interdependent. ​

We say two things are tightly coupled when they are interdependent and loosely coupled when they are independent.

​Tight and loose coupling are not binary positions, but rather relative terms. Any given architectural choice might make two processes more or less coupled.

​Generally when designing distributed systems anything that makes the system more loosely coupled is desirable. But, no useful software system can be built where all the components are completely decoupled.

If two processes are completely independent they can successfully operate without any kind of coordination with the other process.

​Whenever we introduce dependencies, the processes must coordinate their activities.

This requires some kind of communication between the two processes.

This can result in wasted computation, delays due to latency, and computational errors.

​ Good distributed architectures accomplish their tasks with a minimum of coupling. Good distributed system architects choose architectures that minimize the coupling necessary to get the job done.

​Coupling can occur on multiple levels within a system.

The following table gives some of the choices that can be made at different levels of a system that increased or decreases the level of coupling.

 

So, after all that, you can see that distributed systems may or may not be loosely coupled depending on their architecture.

A Hadoop cluster and Gnutella are both distributed since all the computational processes are not all happening on a single processor.

But the Hadoop cluster is tightly coupled while Gnutella is loosely coupled. Nevertheless, both could be appropriately coupled.

 

S.NO	Loosely Coupled	Tightly Coupled
1.	There is distributed memory in loosely coupled multiprocessor system.	There is shared memory, in tightly coupled multiprocessor system.
2.	Loosely Coupled Multiprocessor System has low data rate.	Tightly coupled multiprocessor system has high data rate.
3.	The cost of loosely coupled multiprocessor system is less.	Tightly coupled multiprocessor system is more costly.
4.	In loosely coupled multiprocessor system, modules are connected through Message transfer system network.	While there is PMIN, IOPIN and ISIN networks.
5.	In loosely coupled multiprocessor, Memory conflicts don’t take place.	While tightly coupled multiprocessor system have memory conflicts.
6.	Loosely Coupled Multiprocessor system has low degree of interaction between tasks.	Tightly Coupled multiprocessor system has high degree of interaction between tasks.
7.	In loosely coupled multiprocessor, there is direct connection between processor and I/O devices.	While in tightly coupled multiprocessor, IOPIN helps connection between processor and I/O devices.
8.	Applications of loosely coupled multiprocessor are in distributed computing systems.	Applications of tightly coupled multiprocessor are in parallel processing systems