Watts what with personal computer power supplies? Part One

By Peter Brownlee
Wednesday, 08 August, 2007

Computer power supply units are now hot components, in more than one sense of the word. Peter Brownlee explores the issues as PSUs double in power - then double again. It used to be that a 250-350 W power supply unit in your personal computer was all you were ever likely to need.

The old rule of thumb of allowing 50 W or so for each attached device (disk drives, graphics card and so on) seemed to work and anyway many devices operated sequentially so that all the power was not needed simultaneously.

As they say in New York, "Fuggedaboutit".

Every time you pick up a computer magazine these days there seems to be a review of the latest super power supply unit. The ugly duckling of the component world has suddenly become hot.

In May 2006 one computer website was sagely advising its readers to "make sure you configure this system with the appropriate power supply. If you want to go with a pair of GeForce 8800 GTX graphics cards (or you think you might like to one day), you'll need an 850 W or greater power supply unit."

"If you go with a pair of GeForce 8800 GTS cards, you can get away with 600 W, but you still might want more juice later".

Less than a year later, the same crowd was suggesting 700 W as the minimum "get away with" wattage.

So what's going on?

As you can see from the earlier quotation, dual higher-powered graphics cards working in tandem simply require more power - and they need it continuously. NVIDIA's SLI and ATI's Crossfire systems each require two suitable (usually identical or at least with identical graphics processing chips) mounted on motherboards that have been designed around this capability and often with extra power input on the motherboard to drive the graphics cards.

This is designed for ultra-gamers, the sort of people who want their graphics rendering (and pretty well everything else) super-fast and who want to run two, three or more monitors at once.

While that may not be you, we have all been down this path before where gamers have relentlessly driven the hardware and software markets to performance levels which over time become standard for everyone else.

If you also consider such developments as CPU maker AMD buying ATI, the push towards high-end graphics capabilities is unlikely to go away any time soon.

And then there is simply the numbers game - are you really going to buy a 'mere' 700 W PSU when there is a 1000 W or, heaven help us, a 2000 W model available for a comparable price?

When the personal computer industry went towards dual-everything - dual core CPUs, dual CPUs on a single motherboard, dual graphics cards connected to dual monitors - the way ahead became clearer.

But what comes after dual?


Pretty soon dual stuff will start to seem a bit old hat as the new quad core CPUs become available from the corner computer bits shop and there now seems to be serious talk about designing motherboards for two dual core CPUs (and they may be here already).

But we keep coming back to a central question - what keeps these components running and stable?

It is the formerly boring power supply unit.

As it is, the power consumption of PCs seems to be getting out of hand. There is now a strong push in the CPU industry to get better performance for each watt of power used. If you are building a high-end super-powered gaming rig then you need a good power supply unit and you simply cannot overestimate the importance of the PSU.

A few years ago another trend picked up; everyone wanted 'modified' PCs. Dull beige-painted PCs had to go and were replaced by super stylish, even bizarrely shaped PCs in black or red or silver with side windows so we could actually look at the PCs' insides and then there were all the flashing lights and super cooling.

So we now have 'designer' cases which let you look inside at a mad tangle of multicoloured cables, connectors and high status printed circuit boards.

Cable modularity - the ability to deploy only the cables and connectors you actually need - helps reduce the clutter inside the case and less clutter means better cooling.

From a consumer point of view, the key factors in recent developments in PSUs have been the need for stable, high-output, high-efficiency power supply and distribution for advanced PC configurations and the option for modularity using only the wires what you need.

We may now be entering an era where total mains circuit load will be a central issue even for domestic and small office/home office PC users.

Power, physical size and heat dissipation are already significant factors for notebook computer designers - and users. With the drive to super graphics we may find notebooks, mobile phones and PDAs will require even better designed and engineered batteries if they are not to do double duty as hand warmers and need recharging every hour.

In fact, the answer to the power problem for PCs may lie more in better design and rethinking the way PSUs actually work rather than in doubling and redoubling wattage in a conventional power supply (and then trying to deal with a device that has the same power requirements as a large domestic electric heater).

In the second part of this article we will look at the power and heat management issues arising from the new generation of PSUs and what you can do to maximise the energy efficiency of your computer systems.

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