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Difference Between Loosely Coupled and Tightly Coupled Multiprocessor System
A computing system which consists of more than two processors is known as a multiprocessor system. Multiprocessor systems are broadly classified into two categories− loosely coupled multiprocessor system and tightly coupled multiprocessor system. In a loosely coupled multiprocessor system, the degree of coupling between different processor is low; whereas a tightly coupled multiprocessor system has high degree of coupling between different processors of the system.
Read this article to find more about loosely coupled and tightly coupled multiprocessor systems and how they are different from each other.
What is a Loosely Coupled Multiprocessor System?
A multiprocessor which has very low degree of coupling among different processors of the system is known as loosely coupled multiprocessor system. A loosely coupled multiprocessor system consists of its own local memory, a set of I/O devices, and a channel and arbiter switch. One processor with its local memory, a set of I/O devices and a CAS is referred to as a computer module.
In a loosely coupled multiprocessor system, a message transfer system (MTS) is used to exchange the information between different computer modules of the system. A loosely coupled multiprocessor system is also known as a distributed system.
We obtain higher efficiency from a loosely coupled multiprocessor system, when the processes executing on different computer modules need less interaction. The major drawback of the loosely coupled multiprocessor system is that it has very low throughput.
What is a Tightly Coupled Multiprocessor System?
A multiprocessor which has very high degree of coupling among different processors of the system is known as a tightly coupled multiprocessor system. The important parts of a tightly couple multiprocessor system includes processors, I/O channels, and shared memory modules.
Tightly coupled multiprocessor systems are efficient for real−time or high speed processing applications, but they experience more memory conflicts. These systems have sets of three interconnected networks namely PMIN (Processor−Memory Interconnection Network), IOPIN (I/O Processor Interconnection Network), and ISIN (Interrupt−Signal Interconnection Network). A tightly coupled multiprocessor system has high data rate.
Tightly coupled multiprocessor systems are relatively more expensive than loosely coupled multiprocessor systems.
Difference between Loosely Coupled and Tightly Coupled Multiprocessor Systems
The following table highlights all the major differences between Loosely Coupled and Tightly Coupled Multiprocessor Systems −
| S. No. | Loosely Coupled Multiprocessor System | Tightly Coupled Multiprocessor System |
|---|---|---|
| 1. | In this system, every processor has its own memory module. | In this system, the processors share memory modules. |
| 2. | It is efficient when there is less interaction between tasks running on different processors. | It is efficient when used with real−time processing. |
| 3. | There are no memory conflicts in general. | It has memory conflicts. |
| 4. | It is considered as a Message transfer system (MTS). | They are connected through networks such as PMIN, IOPIN, and ISIN. |
| 5. | It is less expensive. | It is expensive. |
| 6. | It has a low data rate. | It has a high data rate. |
| 7. | It provides comparatively slow speed. | It provides high speed. |
| 8. | They are usually seen in distributed computing systems | It is usually seen in parallel processing systems. |
Conclusion
Both systems are quite different from each other in many aspect, as elaborated in the above table. The most significant difference between loosely coupled and tightly coupled multiprocessor systems is that, in a loosely coupled multiprocessor system, each processor has its own memory module; whereas in a tightly coupled multiprocessor system, all the processors use shared memory modules.
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