Difference between Loosely Coupled and Tightly Coupled Multiprocessor System

A multiprocessor is that which contains more than two processors in a system. Two types of multiprocessor systems are mainly tightly coupled and loosely coupled. The degree of coupling between CPUs is high in a tightly coupled system. In contrast, the degree of coupling between the CPU is low in a loosely coupled system. The main distinction between these coupled systems is that a loosely coupled system contains a distributed memory. On the other hand, the tightly coupled system has a shared memory.

In this article, you will learn about the difference between loosely and tightly coupled systems multiprocessor systems. But before discussing the differences, you must know about the loosely and tightly coupled system multiprocessor system.

What is a loosely coupled system?

A multiprocessor is that which contains more than two processors in a system. A system is known as a loosely connected multiprocessor if there is a very low degree of coupling between these CPUs. Every CPU has its local memory, collection of input-output devices, and channel and arbitrator switch (CAS) in a loosely coupled system. A computer module is a term used to describe the CPU along with its local memory, set of input-output devices, and CAS.

Processes that run on various computer modules exchange messages with one another via a physical section of the message transfer system (MTS). The term "distributed system" also refers to a loosely coupled system. A loosely coupled system is effective when the interactions between the processes running on various computer modules are minimal.

When two or more computer modules make simultaneous requests to access MTS, the CAS chooses one of the requests responsibly and delays the others until the selected request has been serviced completely. All of the system's CPUs have access to the high-speed communication memory that is included in the CAS, and the CAS uses the communication memory to buffer message transfers.

What is a tightly coupled system?

A tightly coupled system is a system architecture and computing method in which all hardware and software components are linked together so that every component is dependent on the others. Tightly coupled system architecture encourages application and code interdependence. It is most commonly used in business systems and applications that rely on the interconnection and inter-processing of two or more systems at the same time to offer a cohesive and integrated solution.

If multiple systems in a tightly coupled system transmit a task, the entire system would typically require to be powered down to resolve a serious hardware issue. For instance, a tightly coupled system would need to be shut down in a multiprocessing environment where multiple computers share the workload to add or replace a system.

The logic of a tightly coupled system is typically distributed among multiple hardware and software components, all of which must be functioning and connected to deliver the business logic and process. For instance, a bank ATM relies on the hardware, built-in firmware and applications, and the main banking app to enable a consumer to withdraw cash or use ATM-specific services. The ATM will not function if any of these components fail.

Key differences between Loosely Coupled and Tightly Coupled Multiprocessing System

There are various key differences between Loosely Coupled and Tightly Coupled system Multiprocessor systems. Some main differences between Loosely Coupled and Tightly Coupled systems are as follows:

1. A loosely coupled system is very effective when the processes executing on separate CPUs have less interaction between them. In contrast, the tightly coupled system may manage a high degree of interaction between processes and is very useful for high-speed and real-time processing.
2. The Message Transfer system (MTS) is the interconnecting network in the loosely coupled system. In contrast, the interconnection networks in a tightly connected system are the IOPIN (the I/O-processor interconnection network), PMIN (the processor-memory interconnection network), and ISIN (the interrupt-signal interconnection network).
3. The tightly coupled system is more expensive but smaller in size. In contrast, the loosely system is less costly but bigger in size.
4. The loosely coupled system contains distributed memory. On the other hand, a tightly coupled system has a shared memory.
5. The loosely coupled system contains a low data rate. On the other hand, the tightly coupled system contains a high data rate.
6. Memory conflict is rare in loosely coupled systems. On the other hand, memory conflict is common in tightly coupled systems.
7. Loosely connected multiprocessor applications are used in distributed computing systems. On the other hand, tightly connected multiprocessor applications are found in parallel processing systems.
8. The CPU and Input/Output devices are directly linked in a loosely coupled multiprocessor. On the other hand, IOPIN aids with the connection of the CPU and I/O devices in tightly coupled multiprocessors.

Head-to-head comparison between Loosely Coupled and Tightly Coupled Multiprocessor System

Here, you will learn about the head-to-head comparison between the loosely coupled and tightly coupled multiprocessor systems. Some main differences between the loosely coupled and tightly coupled multiprocessor system are as follows:

Conclusion

Loosely and tightly coupled, both are multiprocessor systems. The distributed memory in the loosely coupled system delays the data rate, whereas the shared memory in the tightly coupled system accelerates the data rate.