Difference between Loosely Coupled and Tightly Coupled Multiprocessor System

When it comes to multiprocessor system architecture, there is a very fine line between loosely coupled and tightly coupled systems, and this is why that difference is very important when choosing an architecture for a specific system. A multiprocessor system is a system in which there are two or more processors which operate in parallel to execute tasks and generally results to increased computing velocity, trust and efficiency. The relationship that exists between processors is essential in understanding how processors interact, share resources and perform tasks.

Loosely Coupled Multiprocessor System

It is a type of multiprocessing system in which, There is distributed memory instead of shared memory. In loosely coupled multiprocessor system, data rate is low rather than tightly coupled multiprocessor system. In loosely coupled multiprocessor system, modules are connected through MTS (Message transfer system) network.

Advantages of Loosely Coupled Multiprocessor Systems

• Scalability: Scalability is one of the major benefits which can be achieved with the help of loosely connected systems. Additional resources that are required by the processors can be incorporated into more systems without radical impacts on organizational performance.
• Fault Tolerance: Since each processor runs separately, then failure of some processors may not hinder the functioning of the other processors. This improves system reliability.
• Flexibility: Such processors can support different operating systems and other applications that can make the overall process more flexible when it comes to performing various tasks}.
• Cost Efficiency: Loosely coupled systems, therefore, are always cheaper to implement since they may well incorporate commodity hardware that may be bought directly off the shelf and this inter-processor communication does not have to be special.

Disadvantages of Loosely Coupled Multiprocessor Systems

• Latency in Communication: Inter processor communication is slower as compared to processor to core or core to core communication due to network based paradigm which results in more latency.
• Synchronization Overhead: Any work that involves tight coupling between processors will suffer from overheads of synchronizing often across a network.
• Inefficiency for Shared Tasks: Since sharing of memory is awkward, loosely coupled systems are not well suited to tasks which demand high level of inter-processor communication and shared among them resources such as memory.

Tightly Coupled Multiprocessor System

It is a type of multiprocessing system in which, There is shared memory. In tightly coupled multiprocessor system, data rate is high rather than loosely coupled multiprocessor system. In tightly coupled multiprocessor system, modules are connected through PMIN, IOPIN and ISIN networks.

Advantages of Tightly Coupled Multiprocessor Systems

• Faster Communication: This is because the different processors that implement a shared memory design and are interconnected via a high speed buses, have mechanisms that allow for highly efficient methods of communication.
• Efficient Resource Sharing: Tightly coupled systems are closely connected such that resource, for instance, memory and I/O devices can be easily shared; this occurs in instances where information has to be swiftly conveyed among the processors.
• Better Performance for Synchronized Tasks: For the tasks, which involve a lot of interactions and synchronization, for instance, call centers or dispatch offices, it is suggested that tightly coupled systems show better results as opposed to the loosely coupled systems.

Disadvantages of Tightly Coupled Multiprocessor Systems

• Cost: A tightly coupled system is costly to implement because the nodes in the system demand customized media, as well as fixed high-speed connection equipment.
• Scalability Limitations: As Schmidt et al and others have described, tightly-coupled architectures excel at coordinated tasks, allowing multiple processors to work together perfectly, yet this makes the addition of more than one or two of these processors a problem since the newly appended processor shares various resources such as memory and must synchronize the flow of work with all the other processors.
• Failure Impact: There is a tendency to expect one processor or a shared component to fail and may eventually cause failure of the entire system which decreases reliability.

Difference between Loosely Coupled and Tightly Coupled Multiprocessor System

Conclusion

Loosely coupled and tightly coupled multiprocessor systems are designed for particular purposes, the former is good at scalability and fault tolerance while the latter is capable of high-speed communication and good at resource sharing. This is because the selection of these architectures depends with the task and duty of the model or the application at hand in regard to the scalability, cost, speed and sharing of resources in the network. Loose coupled systems are ideal for tasking that will hardly involve much interaction between the processors while in the case of tasks that will need much of the processors’ interacting then a tightly coupled system is desirable.