[quote]The speed of the secondary card in-general also seems to have some impact on performance. I upgraded my secondary card from an 8400GS to a 9800GT (so I could also use it as a dedicated PhsX card) and saw my minimum frame rate increase by about 5FPS across the board.
I thinks thats because of the 9800GTs PhysiX feature.
Please try it with PhysiX on and off!
The 5FPS boost was across the board, even in games that don't use PhysX at all (such as Fallout 3).
[quote]I can't tell if that performance boost came from the 9800GT's faster internal memory interface,
The memory of the second card is absolutely unused when using softth.
The Bitmap image comes from the System Ram, goes through the second cards GPU to the monitor. without any delay (regulary).
Graphiccard VRam is only used/needed when a graphiccard is rendering any videomaterial. but the second graphiccard in a softth-array is just idling (more or less) :D
Sorry, no. The pre-rendered frames being sent from system RAM must first be stored in the video card's onboard RAM before they can be displayed. The framebuffer is still used.
This can actually lead to integrated video cards (the ones that share system RAM) being faster for SoftTH, because your chipset will just shift the addresses around so the integrated video card can access the required information instead of sending all that data across the PCIe bus to a secondary card.
[quote]or if it's because the 8400GS was PCIe 1.0 and the 9800GT is PCIe 2.0 (offering double the PCIe bandwidth).
I'm not sure but i don't think the bandwidth can improve fps at all...
Bandwidth is everything for SoftTH. You're sending 60 frames every second across the PCIe bus and through system RAM (in two directions no less), that requires a lot of bandwidth. Games are also using that same pipe to load themselves onto your primary video card, leaving even less room for SoftTH.
People have shown fairly large performance gains with SoftTH by overclocking their system RAM and the PCIe bus. I can confirm that going from DDR2 800 to DDR2 1066 provided some nice SoftTH performance gains, so it's no stretch of the imagination that upgrading from a PCIe 1.0 to a PCIe 2.0 card (double the PCIe bandwidth) would also help.