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G92: Nvidia GeForce 8800 GT
Author: Tim SmalleyPublished: 2nd November 2007
Connectivity and Power:
On the PCI bracket, there are two dual-link DVI ports which both support HDCP over dual-link like the GeForce 8600-series and there's also an HDTV-Out DIN connector. We asked Nvidia about HDMI support for media centre PCs, and company representatives told us that this would be implemented over the DVI connection.There isn't an audio processor included inside VP2, so this will again be handled via a S/PDIF connector on the PCB. Looking closely at the PCB, the soldering points for this appear to be right next to the SLI finger on the top edge of the board. At this point, it's probably worth making it clear that HDCP is a compulsory part of the GeForce 8800 GT specification – or rather, when the board partners buy GeForce 8800 GT GPUs, they'll also be given a crypto-ROM as part of the 'kit'.
Moving to the opposite end of the PCB, there is a lone six pin PCI-Express power adapter that needs to be plugged in at all times. This is despite the fact that the GeForce 8800 GT is Nvidia's first graphics card to support PCI-Express 2.0. For those that are vaguely familiar with the interconnect's specifications, you'll know that it allows up to 150W to be drawn through the socket on version 2.0.
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We asked Ujesh Desai, Nvidia's General Manager for GeForce graphics, why this was the case and he told us that it was much simpler to route only 75W of power through the PCI-Express slot for backwards compatibility purposes. It means that regardless of whether the card is plugged into a PCIe 1.1 or PCIe 2.0 motherboard, 75W of power goes through the interconnect and the excess is handled by the supplementary power connector.
As the board consumes around 105W at peak, this means that the PCI-Express power adapter will draw roughly 30W of power when the card is running at full whack. Obviously, overclocking might increase this value somewhat but, providing there is sufficient cooling, the various retail GeForce 8800 GT products on the market should overclock pretty well.
VP2:
While we're mentioning HDCP capabilities, it's worth touching on the second generation video processor that Nvidia has incorporated into G92. If you're not familiar with the capabilities of this new addition, please have a look over our GeForce 8600 GTS review, where we cover the features of PureVideo HD and VP2 in some detail.VP2 is a single programmable SIMD (single instruction, multiple data) processor whose flexibility enables it to be expanded upon in the future. It also allows typically very intensive video processing for movies encoded in H.264 to be offloaded from the CPU onto the GPU. In addition to the VP2 engine, there is also a H.264 bitstream processor (BSP) and an AES128 Decryptor.
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The former has been specifically designed to accelerate two H.264 reverse entropy coding schemes known as Context Adaptive Variable Length Coding (CAVLC) and Context Adaptive Binary Arithmetic Coding (CABAC) – two tasks that are very heavy on the CPU in a purely software environment, especially with CABAC. The latter, the AES128 engine, accelerates the decode of the AES128 encryption protocol required by video content security schemes like Advance Access Content System (AACS) and the Windows Vista Media Foundation. Both of these schemes require video data (both compressed and uncompressed) to be encrypted when it is sent over a User Accessible Bus (UAB), like PCI-Express.
Image Quality Improvements:
Nvidia has been hard at work recently trying to improve the transparency anti-aliasing technique it first introduced with the GeForce 7-series GPUs. The transparency multi-sampling anti-aliasing technique resulted in a very small loss in performance, but wasn't that effective in most scenarios.On the other hand, transparency super-sampling delivered much better and more consistent image quality, but this came at the expense of performance - super-sampling is an incredibly expensive 'brute force' method of reducing aliasing.
With the drivers that shipped with the GeForce 8800 GT, Nvidia has enabled a new transparency multi-sampling algorithm that it says helps to remove the compromises. However, due to the short time we've had with this hardware, we haven't had chance to look at this fully yet, but we have included some screenshots that were provided by Nvidia and help to show the differences between the previous transparency multi-sampling implementation to the new implementation. The differences look quite stark, but we'll reserve final judgement on this until we've had a closer look at ourselves.
The good news is that because this is a change at the driver level, any hardware that supports transparency anti-aliasing will be able to utilise the new algorithm - this includes anything released after the GeForce 7800 GTX. To enable the new mode, simply select transparency multi-sampling in with the latest drivers on Nvidia's website.
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