8. Multi-core

As we have discussed earlier, there is now a practical limit to how fast a standard CPU can run due to the sheer heat the CPU generates. Typically this is about 3.5GHz.

Caches can help maximise instruction and data flow. But how to improve performance even further?

The answer is to place multiple processing cores within a single chip and run them independently. For example, if a computer is running multiple applications that are largely independent of one another, then the operating system can allocate each application to run on a different core.

For example, an Intel high end desktop processor has the following specification:

This chip costs around $1000 (£640), before even counting in the rest of the computer - hence the word 'high end'. It is running at 3.5GHz, and has 20Mb of cache but in addition it has 8 independent processing cores. Note that it consumes 140 Watts (TDP column), which is equivalent to about 1/5th of an electric bar fire squished into a space of about 1/4 inch square. This is why it needs sophisticated cooling to stop it simply melting.

Compare this to their high end processor designed for mobile use where a reasonable battery life is a key issue.

It costs about $650 (£416). Now the cache has dropped to 6Mb and there are only 4 cores. But the power consumption has dropped from 140 Watts down to 47 Watts.

This is the kind of compromise chip makers have to make in order to aim at a specific market such as desktop vs. mobile. There is nothing superior about any of them - the chip designer is trying to give maximum benefit to the customer within the constraints.

And finally, there is the market for a cheap and cheerful component for low cost equipment

This costs 1/10th of the price of the mobile device at $47 (£30) but now the cache has dropped to 1Mb and the clock has dropped to 1.86GHz and it only has 2 cores. On the plus side, power has now dropped to 10 Watts.

But even this is fine for everyday use such as a customer wanting to check email and surf the net (such as myself on the move with a compact netbook) but probably not a good idea for a professional trying to video edit the latest Blu-Ray spectacular. But of course, such a customer would not be looking at this end of the market in the first place.