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4. Multiple Processors

Moving on from an array processor, where a single instruction acts upon multiple data sets, the next level of parallel processing is to have multiple instructions acting upon multiple data sets.

This is achieved by having a number of CPUs being applied to a single problem, with each CPU carrying out only part of the overall problem.

A good example of this architecture is a supercomputer. For example the massively parallel IBM Blue Gene supercomputer that has 4,098 processors, allowing for 560 TeraFlops of processing. This is applied to problems such as predicting climate change or running new drug simulations. Large problems that can be broken down into smaller sub-problems.

But even the humble CPU chip in your personal computers is likely to have multiple cores. For example the Intel Core Duo has two CPUs (called 'cores') inside the chip, whilst the Quad core has four.

A multi-core computer is a 'Multiple Instruction Multiple Data' computer or MIMD

Limitations of multi-core processing

This architecture is dependent on being able to cut a problem down into chunks, each chunk can then be processed independently. But not many problems can be broken down in this way and so it remains a less used architecture.

Furthermore, the software programmer has to write the code to take advantage of the multi-core CPUs. This is actually quite difficult and even now most applications running on a multi-core CPU such as the Intel 2 Duo will not be making use of both cores most of the time.