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NVIDIA's GeForce 7800 GT graphics cards


Subtract the X—and a hundred bucks or so
— 8:00 AM on August 11, 2005

IF YOU'VE PURCHASED a GeForce 7800 GTX in the six weeks or so since its introduction, you may want to avert your eyes. If you purchased a Radeon X850 XT in recent months, just close your browser window now. And if you're a corporate executive at a certain Canadian fabless semiconductor firm, you may want to bury your head. NVIDIA is now unleashing a card based on an ever so slightly cut down version of the G70 graphics processor at a substantial discount off the price of the GeForce 7800 GTX.

An army of cooling fans has been whirring nonstop here in Damage Labs for the past week or so to bring you an extensive set of benchmarks of the GeForce 7800 GT. The short version? The 7800 GT offers near-GTX performance for at least a hundred bucks less than NVIDIA's top-end card, and it pretty much creams anything else in its price range. Keep reading for the full story.

What makes a GT
For those of you familiar with the GeForce 7800 GTX, getting a handle on the GT will be easy. If you're unfamiliar with the 7800 GTX, well, then you need to go read our mind-enhancing review of NVIDIA's seventh-gen GPU. The GeForce 7800 GT is based on the same G70 graphics processor that powers the GTX, but NVIDIA has disabled a few of the chip's functional units for this less expensive card. I have done violence to a block diagram of a G70 GPU in order to illustrate what's been disabled. Have a look:

Up top there, you can see that one of the G70's eight vertex shader units, responsible for geometry processing, is crossed out with a big, red "X." This vertex unit is not functional in the 7800 GT, so the other seven will have to do. Across the middle, one of the six pixel-pipeline "quads" is crossed out, leaving the GeForce 7800 GT with a total of 20 pixel shader units. Without the services of these deactivated vertex and pixel shader units, the 7800 GT will perform a little bit slower than the 7800 GTX.

NVIDIA has also lowered the recommended clock speeds for the 7800 GT. A bone-stock GeForce 7800 GTX runs its GPU at 430MHz and its GDDR3 memory at 600MHz, while stock frequencies on the GT are 400MHz for the GPU and 500MHz for memory. Beyond that, little else has changed. The 7800 GT still has sixteen ROPs capable of writing one pixel per clock to memory, and it still has a 256-bit memory interface.

The cards
None of the GT's spec changes should hamper its performance too much. The thing has more and better pixel pipes than a GeForce 6800 Ultra, for goshsakes. Still, NVIDIA's board partners are already starting to push past the recommended specs, as they've done with the 7800 GTX. Two of the three brands represented in our recent 7800 GTX roundup sell "overclocked in the box" cards, and some of the same suspects are tuning up the GT. BFG Tech's GeForce 7800 GT OC, for instance, will sell with a 425MHz GPU and 525MHz memory. Meanwhile, the XFX cards we received for review are clocked at 450MHz with 525MHz memory.


XFX's GeForce 7800 GT

In terms of basic layout and cooler design, I'd expect at least the first wave of 7800 GT cards to be entirely similar to the XFX card pictured above. At first glance, this looks very much like a 7800 GTX—same PCI Express connector, same dual DVI ports, same video in/out connector, same six-pin auxiliary power input. However, the 7800 GT board is actually about a half-inch shorter than a 7800 GTX, and the cooler is downsized, as well. That doesn't mean, of course, that the 7800 GT is a smallish card; it's still about an inch longer than a Radeon X850 XT Platinum Edition. It is smaller than a GTX, though.

Board makers aren't just overclocking NVIDIA's GeForce 7-series cards; they're also underclocking prices. NVIDIA's initial estimated price on the 7800 GTX was $599, but cards are already selling for as low as $499 at online vendors. That's no bargain, but it ain't $599, either. In the same vein, I'd expect board makers to undercut NVIDIA's suggested $449 list price somewhat on the 7800 GT. In fact, XFX says it will have its "overclocked in the box" 7800 GT selling at multiple online vendors, today, at $399.