The GeForce 8800 GTX wasn't only the first GPU for PC graphics cards that supported DirectX 10 and Shader Model 4, it was also the first to introduce the idea of a unified shader architecture. This means that rather than having a fixed number of pixel processors and vertex pipes, as is the case with a DirectX 9 GPU, a GPU with a unified shader architecture has a number of general-purpose stream processors that can perform pixel and vertex calculations.
This is important since, depending on the type of game or scene, some parts of a DirectX 9 GPU will be underutilised some of the time. For example, some pixel processors may be idle when the GPU is rendering a scene with complex geometry (which is processed by the vertex pipes). Alternatively, some vertex pipes may be idle when the pixel processors are busy working on pixel shader-intensive tasks, such as procedurally generated textures and lighting calculations. In contrast, the shader processors in a unified shader architecture can be allocated to vertex or pixel work according to demand.
Currently, there are four models in the 8800-series, ranging all the way from £190 to £500. As their names suggest, the 320MB 8800 GTS and 640MB 8800 GTS are identical apart from their quantities of on-board memory. The GPU on both cards is clocked at 500MHz, although the 96 stream processors run much faster at 1.2GHz. The GDDR3 memory runs at 800MHz (1.6GHz effective) and is accessed by a 320-bit memory bus.
Both cards perform well at low and medium resolutions. The 320MB 8800 GTS is able to play all three test games at 1,680 x 1,050 with AA and AF enabled. However, due to its additional memory, the 640MB 8800 GTS pulls ahead of the 320MB 8800 GTS at higher resolutions, managing to achieve a smooth frame rate in all three games at 1,920 x 1,200 with AA and AF enabled, a feat that it's nearest-priced competitor, the Radeon HD 2900XT, can't manage. Because of its additional memory, the 640MB 8800 GTS also consumes up to 20W more than the 320MB version in our test rig.
Further up the 8800-series food chain is the 8800 GTX; up until the release of the 8800 Ultra a few weeks ago, this was the most powerful graphics card on the planet. Both GPUs have 128 stream processors, with 768MB of RAM and a 384-bit memory bus, but they run at different clock frequencies. The GPU of the 8800 GTX runs at 575MHz, although the stream processors are clocked much higher at 1.35GHz, while the RAM runs at 900MHz (1.8GHz effective). The Ultra is architecturally identical to the 8800 GTX, but its GPU runs at 612MHz, the stream processors at 1.5GHz, and the RAM at a whopping 1.08GHz (2.16GHz effective). Despite these high frequencies and the huge amount of on-board RAM the 8800 GTX and Ultra are comparatively power efficient, drawing up to 60W less than the Radeon HD 2900XT.
As the 8800 GTX and 8800 Ultra run at such high frequencies and have more RAM than the cheaper 8800-series cards, they're much better performers. However, you'll only see the benefit of an 8800 GTX or 8800 Ultra when gaming at 1,920 x 1,200 or higher, as the 320MB 8800 GTS and 640MB 8800 GTS are more than capable of playing any current game at lower resolutions. The 8800 GTX and 8800 Ultra are also a lot more power-hungry than the 8800 GTS cards, as both need two 6-pin PCI-E plugs, as opposed to the single plug required by the GTS cards.
Given the £140 price difference between an 8800 Ultra and 8800 GTX, it's difficult to justify the cost of the flagship card, especially as it's barely any faster. For those who don't have the stomach for a £500 graphics card, the £190 320MB 8800 GTS is an amazing bargain, especially as DirectX 10 games are finally beginning to appear.
Author: James Gorbold and Chris Lee
NVIDIA GeForce 8800 GTS 320MB