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What are the multiprocessor systems?

Multiprocessing involves more than one processor or CPUs (central processing units) in one system.
– If a system supports multiprocessing it means that it has the ability to support many processors and is capable of dividing tasks between them.
– With the context and how CPUs are defined, the definition of the multiprocessing also changes such as:

  • Multiple cores in one die.
  • Many dies in one package
  • Many packages in one CPU and so on.

What do you call the execution of many software processes in a single processing unit that are concurrent? Of course this is multiprocessing even though multi–programming and multi–tasking more appropriately define this concept. But these two suit well to the processing software. But multiprocessing refers to the use of multiple hardware units. It is possible for the systems to have both qualities of multi–programming and multi–processing or any one of these.

Types of Multiprocessing Systems

1. Processor Symmetry:
– In a multiprocessing system, it is possible that all the processors might be assigned an equal status or some might be assigned special purposes.
– Symmetry of a given system is determined by the combination of software design of the operating system and hardware. – For example, for responding to all the hardware interrupts, only one processing unit might be required by the hardware and software considerations.
– On the other hand, all the tasks of the system might be divided equally between the various processors.
– In some cases certain restrictions might such as only one particular CPU would execute the kernel code and another combination of processors might execute the user code.
– These kinds of restrictions are imposed, then it becomes easy for designing the multiprocessor systems.
– But then also the efficiency of these systems remains less when compared to the systems where all the processors are utilized.
– Systems in which all the processors are treated the same are called the SMP systems or the symmetric multiprocessing systems.
The remaining systems might be classified in to the following three categories:
– Clustered multiprocessing
– NUMA (non – uniform memory access) multiprocessing and
– ASMP (asynchronous multiprocessing) systems.

2. Processors have the capability of executing a sequence of instructions in to many contexts such as multiple data, single instruction etc. or vice versa such as in single data, multiple instruction etc. The former finds use in vector processing and the latter in redundancy. Both of these might be applied for describing the hyper-threading or pipe lined processors.

3. The multiprocessor systems where the multiple CPUs are connected to each other at bus level are said to be tightly coupled. A central shared memory is accessed by all these CPUs.

4. In chip multiprocessors, many processors are placed on the same chip and is extreme form of tightly coupled multiprocessing.

5. The other type of multiprocessor systems are the loosely coupled multiprocessor systems that are often called clusters. These systems are based up on many standalone single processors that are connected to each other via some high speed communicating system. For example Beowulf cluster.

The former types of systems are much better than the latter ones since they are physically smaller and perform better. There drawbacks are that they require high initial investments and a rapid depreciation is possible. The loosely coupled systems are quite inexpensive when compared to their tightly coupled counterparts. Plus, they can be used as individual units once they are no more in use of the cluster. Where tightly coupled systems eat less energy, the loosely coupled machines consume more because of their large number of components.

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