The Card & 7800 GT GPU
When the GeForce 6800 GT was introduced, it was basically a lower clocked version of the 6800 Ultra, with a slimmer single-slot cooler. However, the GeForce 7800 GT isn't simply a lower-clocked version of the GeForce 7800 GTX. There are actually quite a few areas where NVIDIA's latest top-of-the-line products differ. We'll explain a few of the differences a little later, after we show you how the raw capabilities of the GeForce 7800 GT stack up versus the last year and a half of ATI's and NVIDIA's high-end products.
|*Newer GeForce 6800 Ultras are clocked at 425MHz
**The 7800 GT/GTX have 16 ROPs, hence the lower than expected Pixel Fillrate
As you can see, the GeForce 7800 GT compares favorably with its competition, although the "paper" specifications make it seem like ATI's X850 series of products have the upper hand in terms of raw performance characteristics. As you'll see later, this doesn't play out in real-world testing. NVIDIA's reference specifications call for the 7800 GT's 20-pipe GPU to be clocked at 400MHz, with 256MB of 1GHz (500MHz DDR) GDDR3 RAM, which results in a peak pixel fillrate of 6.4GPixes/s (16 ROPs x 400MHz), 8GTexels/s (textured pixels), and 32GB/s of memory bandwidth. NVIDIA's partners won't necessarily be sticking to the reference specifications though and as we noted earlier, the XFX board we tested didn't. In fact the XFX GeForce 7800 GT we tested had its core clocked at 450MHz, with it's memory clockced at 1.05GHz. But don't worry -- we tested it at reference speeds too, just in case retail cards ship with clock speeds somewhat lower.
We should explain that because NVIDIA has re-architected the G70's pipelines and memory controller for efficiency and higher performance, the GeForce 7800 GT is actually capable of outperforming products that seem to have an advantage on paper. Our performance analysis on the proceeding pages doesn't exactly jibe with these "theoretical" peak performance numbers.
Right away, just by looking at the new GeForce 7800 GT, you can see that it's quite different than the GeForce 7800 GTX. Unlike the GTX, the GT does not have any memory chips populating the back-side of the card and its cooling apparatus is a completely different shape. The GT's cooler is taller, but it's not quite as wide. The 7800 GT also has a completely different voltage regulator configuration, that doesn't require any additional cooling / heatsinks. In fact, the GeForce 7800 GT is even based upon a completely new PCB design, that is about a quarter of an inch smaller than the GeForce 7800 GTX. We asked NVIDIA why they decided to go with a different PCB for the GT, and weren't given a direct answer, but we suspect it's a cost saving measure and could perhaps prevent modding the card into a pseudo-7800 GTX. Time will tell.
In addition to the physical differences, the GeForce 7800 GT and GeForce 7800 GTX have some architectural differences as well. For example, the GeForce 7800 GTX has six, four-pixel pipeline quads, for a total of 24 pixel-pipelines. The GeForce 7800 GT however, has one less quad enabled, for a grand total of 20 pixel-pipelines. The GT also has one less vertex pipeline; there are 7 vertex pipes enabled in the GT, as opposed to 8 in the GeForce 7800 GTX. The GT and GTX don't differ in any other ways, other than what we've explained here though. At the heart of each card is the same .11 micron G70 GPU, and they each have the same base feature-set.