The 8800 GTX and GTS
For G80 NVIDIA has currently planned two card SKUs for today’s launch: the GeForce 8800 GTX, and the GeForce 8800 GTS. We’ve gone over some of the key differences between the two GPUs on the previous pages, but this chart sums things up nicely:
|GeForce 8800 Series Specs|
|GeForce 8800 GTX||GeForce 8800 GTS|
|# of Transistors||681M||681M|
|Core Clock (including dispatch, texture units, ROPs)||575MHz||500MHz|
|Shader Clock (Stream Processors)||1350MHz||1200MHz|
|# of Shaders (Stream Processors)||128||96|
|Memory Clock||900MHz (1.8GHz effective)||800MHz (1.6GHz effective)|
|Memory Bandwidth (GB/s)||86.4GB/sec||64GB/sec|
|# of ROPs||24||20|
|Price||$599 MSRP||$449 MSRP|
As you can see, the transistor count between the GeForce 8800 GTX and 8800 GTS is the same, this is because they’re both the exact same G80 GPU. As we outlined earlier, the key difference is that NVIDIA disables two banks of stream processors, that’s 32 shaders total. This cuts the number of functional shading units down from 128 in GeForce 8800 GTX down to 96 in GeForce 8800 GTS. NVIDIA also disables one ROP.
Clock speeds and the memory subsystem are also slightly different between the two cards, as the GeForce 8800 GTX core clock speed is 575MHz versus 500MHz in the GeForce 8800 GTS, while the shading units on the GTX board run at 1350MHz versus 1200MHz on the 8800 GTS. NVIDIA also uses a narrower 320-bit memory interface on the GeForce 8800 GTS with 640MB of slower 800MHz memory. The GeForce 8800 GTX boasts a 384-bit memory interface outfitted with 768MB of memory running at 900MHz. And of course, you’ll no doubt notice the difference in price.
The boards themselves are completely different as well:
As you can see, NVIDIA’s incorporated a black PCB for the GeForce 8800 reference design (a first for an NVIDIA reference board), with dual-slot cooling on both the GeForce 8800 GTX and the 8800 GTS. The GeForce 8800 GTX is slightly longer than the GeForce 8800 GTS, its PCB is 10.5” long versus 9” for the GeForce 8800 GTS, and as it has been widely reported prior to today’s launch, the GeForce 8800 GTX sports dual PCIe power connectors. We asked NVIDIA why the need for two power connectors and were told that the max TDP requirement for the GeForce 8800 GTX is 177W. According to NVIDIA though, this is a worst case scenario where every functional unit on the GPU is maxed out, and doesn’t happen in typical gaming sessions where their own testing has shown GPU power usage in the 116W-120W range on average and 145W as the high point.
Since each external PCIe power connector on the card itself is capable of supplying up to 75W to the card, and the PCIe slot itself also maxes out at 75W, this isn’t quite enough juice for the 177W TDP, hence the need for the second external PCIe power connector. By adding the second connector, this gives NVIDIA plenty of headroom on the 8800 GTX. And by the way, max TDP on the 8800 GTS is 147W, so it’s able to get by with just one PCIe power connector.
In terms of power requirements, NVIDIA’s power guidelines call for a minimum of a 450W power supply for the GeForce 8800 GTX (capable of supplying 30A on the 12V rail) and a 400W power supply for the GeForce 8800 GTS (with a current rating of 26A on the 12V rail).