Two are sometimes better than one, a tenet that Asus is trying to prove with its Extreme N7800GT Dual graphics card. This features not one but two Nvidia GeForce 7800GT cores on the same PCB.

But - and there always has to be a but - you have to have the right motherboard to support it, enough space to fit it and pockets deep enough to afford it. There's also the problem of finding one, as Asus is, for the moment, only producing 2,000 units.

This isn't the first card to have dual core SLI GPUs on the same PCB (Gigabyte tried it a while back), but this is certainly the most powerful GPU to date to be used in this way.

Asus hasn't stopped there: not only are there two cores, but the cores have been tweaked so that they are clocked at 430MHz, which is 30MHz faster than standard. The card comes with 256MB of GDDR3 memory per GPU, although no single core can use the 512MB total. The memory itself is composed of Samsung GC16 modules which are rated at, and run at, 600MHz (1.2GHz effective); a massive 200MHz faster than standard.

As you can imagine, the performance of the N7800GT Dual is outstanding. Comparing it to Asus's 7800GT, the single core card manages a 3DMark score of 6,790 while the N7800GT Dual wades in with a whopping 9,560. This is faster than a single card 7800GTX, even the 512MB version, but slower than a 7800GTX SLI setup.

At higher resolutions using real games the N7800GT Dual shows its clout with frame rates of 83.7 and 53.89 for Doom3 and FarCry respectively, with all details set to maximum and running at a 1,600 x 1,200 resolution with 4x Anti Aliasing and Aniscopic filtering.

It's one of the few cards around for which you have to take its size in consideration, though, as this beast measures 24.5cm wide by 14.5cm high, which is some 3.5cm higher than a standard card.

As a result, the N7800GT Dual is only compatible with some SLI motherboards. As it stands the list comprises; Asus P5ND2-SLI, A8N-SLI, A8N-SLI Deluxe, A8N-SLI Premium, the new A8N32-SLI Deluxe, DFI's LANPARTY nF4 SLI-DR and Gigabyte's GA-K8NXP-SLI. But no doubt the list will get longer with time.

A unique feature of the N7800GT Dual is the external power supply Asus provides with it. If your power supply can't provide enough power for the card (and you would think that anyone paying for a £600 quid graphics card would have a powerful system to start with), then the 80W external unit will supply all the power the card demands. The cable plugs into the card via a port in its backplane.

Apart from the power input the dual slot backplane contains a VIVO port and two DVI ports. Above these sit two holes for the two VGA ports which come on a separate header, to give a total of four outputs.

On a final note, while this card is noisier than the reference 7800GTX or 7800GTs we've tested, it's certainly no vacuum cleaner.

Asus is to be congratulated for bringing some innovation to the market. There's no doubting the performance of this card, but its size and huge price will be limiting factors to most people.