NVIDIA's GeForce 8800 (G80): GPUs Re-architected for DirectX 10
by Anand Lal Shimpi & Derek Wilson on November 8, 2006 6:01 PM EST- Posted in
- GPUs
The 8800 GTX and GTS
Today we expect to see availability of two cards based on NVIDIA's G80 GPU: the GeForce 8800 GTX and 8800 GTS. Priced at $599 and $449 respectively, the two cards, as usual, differ in clock speeds and processing power.
8800 GTX (top) vs. 7900 GTX (bottom)
The 8800 GTX gets the full G80 implementation of 128 stream processors and 64 texture fetch units. The stream processors are clocked at 1.35GHz with the rest of the GPU running at 575MHz. The GTX has six 64-bit memory controllers operating in tandem, connected to 768MB of GDDR3 memory running at 900MHz. GDDR4 is supported but will be introduced on a later card.
NVIO: Driving a pair of TMDS transmitters near you
You get two dual-link DVI ports driven by NVIDIA's new NVIO chip that handles TMDS and other currently unknown functions. Keeping a TMDS on-die is a very difficult thing to do, especially if you have logic operating at such high clock speeds within the GPU, so with G80 NVIDIA had to move the TMDS off-die and onto this separate chip. The NVIO chip also supports HDCP, but you do need the crypto ROM keys in order to have full HDCP support on the card. That final decision is up to the individual card manufacturers, although at this price point we hope they all choose to include HDCP support.
The 8800 GTX has two PCIe power connectors and two SLI connectors:
Two SLI connectors on the 8800 GTX
Bridges in action
The dual power connectors are necessary to avoid drawing more power from a single connector than the current ATX specification allows for. The dual SLI connectors are for future applications, such as daisy chaining three G80 based GPUs, much like ATI's latest CrossFire offerings.
dual power connectors
The GeForce 8800 GTS loses 32 SPs bringing it down to 96 stream processors and 48 texture fetch units. The shader core runs at 1.2GHz, while the rest of the GTS runs at 500MHz. The GTS also has only five 64-bit memory controllers with 640MB of GDDR3 memory running at 800MHz.
7900 GTX (left) 8800 GTS (middle) 8800 GTX (right)
The 8800 GTS has the same NVIO chip as the 8800 GTX, but the board itself is a bit shorter and it only features one SLI connector and one PCIe power connector.
Only one power connector on an 8800 GTS
...and only one SLI connector
Both cards are extremely quiet during operation and are audibly indiscernible from a 7900 GTX.
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Nightmare225 - Sunday, November 26, 2006 - link
Are the FPS posted in this article, Minimum FPS, Average FPS, or Maximum? Thanks!multiblitz - Monday, November 20, 2006 - link
I enjoyed your reviews always a lot as they inclueded the video-capbilities for a HTPC on previous cards. Unfortunately this was this time not the case. Hopefully there will be a 2. Part covering this as well ? If so, it would be nice to make a compariosn on picture quality as well against the filters of ffdshow, as nvidia is now as well supporting postprocessing filters...DerekWilson - Tuesday, November 21, 2006 - link
What we know right now is that 8800 gets a 128 out of 130 on HQV tests.We haven't quite put together an HTPC look at 8800, but this is a possibility for the future.
epsil0n - Sunday, November 19, 2006 - link
I am not agree with this:"It isn't surprising to see that NVIDIA's implementation of a unified shader is based on taking a pixel shader quad pipeline, and breaking up the vector units into 4 scalar units. Now, rather than 4 pixel quads, we see 16 SPs per "quad" or block of stream processors. Each block of 16 SPs shares 4 texture address units, 8 texture filter units, and an L1 cache."
If i understood well this sentence tells that given 4 pixels the numbers of SPs involved in the computation are 16. Then, this assumes that each component of the pixel shader is computed horizontally over 16 SP (4pixel x 4rgba = 16SP). But, are you sure??
I didn't found others articles over the web that speculate about this. Reading others articles the main idea that i realized is that a shader is computed by one and only one SP. Each vector instruction (inside the shader) is "mapped" as a sequence of scalar operations (a dot product beetwen two vectors is mapped as 4 MUD/ADD operations). As a consequence, in this scenario 4 pixels are computed only by 4 SPs.
DerekWilson - Tuesday, November 21, 2006 - link
Honestly, NVIDIA wouldn't give us this level of detail. We certainly pressed them about how vertices and pixels map to SPs, but the answer we got was always something about how dynamic the hardware is able to dynamically schedule the SPs optimally according to what needs to be done.They can get away with being obscure about how they actually process the data because it could happen either way and provide the same effect to the developer and gamer alike.
Scheduling the simultaneous processing one vec4 MAD operation on 4 quads (16 pixels) over 4 groups of 4 SPs will take 4 clock cycles (in terms of throughput). Processing the same 16 pixels on 16 SPs will also take 4 clock cycles.
But there are reasons to believe that things happen the way we described. Loading components of 16 different "threads" (verts, pixels or whatever) would likely be harder on the cache than loading all 4 components of 4 different threads. We could see them schedule multiple ops from 4 threads to fill up each block of shaders -- like computing 4 consecutive scalar operations for 4 threads on 16 SPs.
At the same time, it might be easier to maximize SP utilization if 16 threads were processed on one block of SPs every clock.
I think the answer to this question is that NVIDIA knows, they didn't tell us, and all we can do is give it our best guess.
xtknight - Thursday, November 16, 2006 - link
This has been AT's best article in awhile. Tons of great, concise info.I have a question about the gamma corrected AA. This would be detrimental if you've already calibrated your display, correct (assuming the game heeds to the calibration)? Do you know what gamma correction factor the cards use for 'gamma corrected AA'?
DerekWilson - Monday, November 20, 2006 - link
I don't know if they dynamically adjust gamma correction based on monitor (that would be nice though) ...if they don't they likely adjusted for a gamma of either (or between) 2.2 or 2.5.
Also, thanks :-) There was a lot more we wanted to pack in, but I'm glad to see that we did a good job with what we were able to include.
Thanks,
Derek Wilson
bjacobson - Sunday, November 12, 2006 - link
This comment is unrelated, but could you implement some system where after rating a comment, on reload the page goes back to the comment I was just at? Otherwise I rate something halfway down and then have to spend several seconds finding where I just was. Just a little nuissance.Thanks for the great article, fun read.
neo229 - Friday, November 10, 2006 - link
This is a very suspect quote. A card that requires two PCIe power connectors is going to dissipate a lot of heat. More heat means there must be a faster, louder fan or more substantial and costly heat sink. The extra costs associated with providing a truly quiet card mean that the bulk of manufacturers go with the loud fan option.
DerekWilson - Friday, November 10, 2006 - link
If manufacturers go with the NVIDIA reference design, then we will see a nice large heatsink with a huge quiet fan.Really, it does move a lot of air without making a lot of noise ... Are there any devices we can get to measure the airflow of a cooling solution?
We are also seeing some designs using water cooling and theres even one with a thermo-electric (peltier) cooler on it. Manufacturers are going to great lengths to keep this thing running cool without generating much noise.
None of the 8 retail cards we are testing right now generate nearly the noise of the X1950 XTX ... We are working on a retail roundup right now, and we'll absolutely have noise numbers for all of these cards at load.