If you've ever wondered why Nvidia's first generation of GeForce GTX 480 cards only featured 480 stream processors, rather than the full set of 512, then we may have just found the answer via a full test of an elusive full-spec card.
As you can probably guess, the card in question is the same PCB with yellow capacitors that's been generating tech headlines for the last couple of days. First came a photo and a couple of GPU-Z screenshots, then came a couple of benchmarks, and now the curious testers at Expreview have finally pulled out all the stops and given the card the nearest you can get to a review.
As well as the usual performance results, the test crucially included power-consumption and temperature measurements, and the results from the former were utterly insane.
Using PSU maker Seasonic's Power Angel tool, the site gauged the power consumption of their whole test bed when it was idle, and when the GPU was running flat-out in FurMark. The results when the machine was idle were unsurprising, with the machine consuming 141W with the standard card, and 158W with the card with 512 stream processors.
However, the difference between the two figures stretched to breaking point as the GPUs started work. According to the site, the machine consumed 440W with the standard card in place, but this rocketed up to 644W with the full-spec card installed. That's a ridiculous amount of extra power for just 32 extra stream processors.
There are a few explanations for this, including the fact that the card with 512 stream processors is an unfinished sample, which requires two eight-pin PCI-E power connectors. It may also be that the results from Power Angel are wrong, and the card needs retesting, perhaps with a different power measurement system.
However, if the results are genuine, then they perfectly explain why Nvidia decided to opt for 480 stream processors on the top chip at launch.
Despite the ridiculous power consumption, the site claims it successfully overclocked the card, which comes from with an Arctic Cooling Accelero Xtreme Plus cooler.
With the GPU running at 850MHz, the shaders clocked at 1,700MHz and the memory running at 4.2GHz (effective), Expreview says the card scored X12173 in 3DMark Vantage, compared with a score of X11371 from the standard GTX 480 at the same clock speeds.
The site also ran benchmarks on a number of other games, including Metro 2033, Left4Dead 2, Far Cry 2, Just Cause 2, Crysis Warhead, DiRT 2 and Battlefield: Bad Company 2.
In general, the performance difference between the full-spec card and the standard GTX 480 appears to widen as you add more anti-aliasing. The highest speed difference was seen in Metro 2033 at 1.920 x 1,200 with 4x anti-aliasing and 16x anisotropic filtering, where the card with 512 stream processors was 9.67 per cent faster than the standard card.
On average, however, the full-spec card was only around 5.67 per cent faster. This is the performance difference you'd expect from an extra 32 stream processors, but you wouldn't expect your system to consume an extra 204W in the process. We'll keep an eye on this one and see if Expreview retests the card's power consumption at a later date.