Page last updated at 10:40 GMT, Thursday, 1 October 2009 11:40 UK

Tech Know: How low can you go?

By Mark Ward
Technology correspondent, BBC News


Ellie Gibson meets the men who pour nitrogen into their PCs to satisfy their need for computing speed.

Paul Watkinson and Barrie Wynd have done about the coolest thing you can do with a computer.

The pair are among the elite of the UK's overclocking community. These folks are not satisfied to use a PC as it is delivered from the factory. Instead, they look for ways to supercharge it.

Typically these tweaks are applied to the core processor because the faster that runs then, usually, the faster the computer can complete all the tasks it is being asked to do.

It is known as "overclocking" because every chip has a clock speed, measured in gigahertz (Ghz) or megahertz (Mhz), which describes how fast it completes a basic operation.

A chip with a clock speed of one gigahertz completes one billion "ticks" per second.

Clock speed is a crude measure of the overall number crunching ability of a PC, but is accepted as shorthand for the horsepower a chip can muster.

As its name implies, overclocking is all about running a chip faster than its basic or stock speed.

Overclocking involves putting a bigger voltage across a chip and means it generates lots more heat.

"A product is designed with a certain thermal restraint and to use a certain amount of voltage," said Mr Watkinson. "Stock voltages are 1.1 volts."

"We're putting 1.6 and 1.7 volts through them so we have to bring the cooling down very low to compensate."

Which is why this is such a cool hobby. Good cooling will mean a chip can run faster without overheating and crashing.

Chill cabinet

Paul Watkinson
Paul Watkinson has been cooling and overclocking for years

Mr Watkinson has been experimenting with different ways to cool overclocked chips for years. He has, he told BBC News, worked his way up the ladder of different cooling methods.

"We all start at the bottom," he said. "We experiment with air cooling then go to water cooling and then coupled water cooling."

Mr Watkinson was lucky enough to have some old beer chillers hanging around so he used those to help cool the water for his chips. He found that when he removed the thermostat the temperature of the chip dropped to about -15°C.

From there he has progressed to more exotic refrigerants.

Probably the most exotic he has used is liquid nitrogen which can cool a chip to -197°C.

"This is for extreme enthusiasts," said Mr Watkinson. "Us guys who do this have a passion for it"

He's not wrong. For a start getting hold of liquid nitrogen is not easy. It cannot be delivered to homes and anyone wanting to buy it must register with commercial gas suppliers and undergo checks before they can buy it.

This is because the substance is classified as a hazardous substance and anyone who does not respect it is likely could come away physically scarred by the experience.

Liquid nitrogen is also expensive. Unlike water cooled systems which are sealed and recirculate the coolant, liquid nitrogen boils off as it is cools.

"It's easy to get through 50 litres a day for just one person," said Mr Watkinson. An amount that costs about £200.

There are also the problems involved with using such a chilly substance. Care has to be taken to ensure that condensation does not pool on a motherboard and short out the computer.

Extreme test

Pouring liquid nitrogen
The pot has to be dosed with the liquid nitrogen

A typical cooling run with liquid nitrogen involves covering a CPU in putty leaving only its upper surface open to the air. Then a thick copper pot, typically weighing several kilos, is placed over it, the computer is started and the liquid nitrogen poured in.

"We use it as waterfall," he said. "It's poured into a metal cylinder and as it hits the chip surface it evaporates."

The first stage, said Mr Watkinson, is to find the "cold lock" level - the temperature beyond which it will not work. Just above that is likely to be the sweet spot for overclocking.

For most PC silicon chips that cold lock is about -120°C.

Once that level is found, said Mr Watkinson, the pot is regularly "dosed" with more coolant to keep the temperature hovering at the right level and the chip is pushed to see what it can do.

There is luck as well as judgement involved with finding a good overclocking chip, he said.

Chip giant Intel sells "extreme editions" of its chips that it claims are the best made and will be able to stand the excesses to which overclocking subjects them. They typically cost far more than a standard Intel chip of the same make.

"You can't do this with everything, it takes some experimenting," said Mr Watkinson. "You can have 10 chips the same and no two will perform the same."

In some cases a 3Ghz chip has been pushed to 6.5Ghz and a successful overclocking run always shows a speed boost.

To measure just how much that boost is, the PC is subject to some benchmark speed tests.

The advent of multi-core chips means that a simple boost to clock speed has a complicated effect on overall horsepower.

"You have processors with eight cores and it's very much more difficult to get them to run faster as you are no longer cooling one core, you are cooling eight," said Mr Watkinson.

James Gorbold, deputy editor of modding mag Custom PC, said: "There's almost no practical application for extreme cooling. It is purely done for the purpose of getting a bigger number in a benchmark score."

For Mr Gorbold, extreme overclocking is the Formula One of the modding world in that it is full of astonishing scenes of engineering prowess, raw power, head-to-head competition, the risk of high-speed crashes and shameless playing to the crowd.


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