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View Full Version : PCI-E 16x video card can run at 4x ???


jbash
04-16-06, 11:25 AM
2 weeks ago my motherboard (ASUS P4PE AGP-4x) and my video card (Leadtek 6800GT AGP-8X) were broken. Argh !

I'm happy with my RAM (2x512MB DDR400 Corsair CL2) and CPU (P4 3.06GHz HT 478pin) so I've replaced only my broken motherboard with a ASUS P4V800D-X (VIA PT880Ultra and VIA 8237R based).
This new mobo support my old CPU and my RAM and has one AGP-8x slot and one physical PCI-E 16x but this slot it's limited at 4x speed max (due to PT880Ultra chipset limitation)
Now I need to buy a new video card: my old was broken too. I think an XFX card based on Nvidia 7900GT GPU like "XFX GeForce 7900GT 256MB DDR3 Extreme Edition PV-T71G-UDE" http://www.xfxforce.com/web/product/listConfigurationDetails.jspa?productConfiguration Id=186017

My question is: a 7900GT video card with PCI-E 16x can work in a PCI-E 16x slot limited to a lower speed (4x) ? Do you remeber AGP ? An AGP-8X card can work in a 8x slot and 4x slot and (perhaps) 1x slot. Is it the same for PCI-E ?

Yes, I know that PCI-E 4x is slower than PCI-E 16x, but for now I'm satisfied.... In the future, if I'll change CPU and mobo with a PCI-E 16x (running really at 16x) I'll have a video card 'PCI-E 16x ready'.....

Thanks in advance...

XDanger
05-29-06, 06:53 AM
i have the same situation as you ,using an agp 6800 on the p4v800d-x at the moment ,looks like a 10% drop in performance is likely but no confirmed benchmark yet , I keep looking. Post any information when you get it please :)

msxyz
05-29-06, 08:34 AM
easily explained... those dual slot motherboards are usually built around chipsets that don't support a 16x port.

The PCI-e connector is compatible with 16x boards but it's just made out of several 1x PCI-e lanes linked together. Chipset like the 915G (or some Via equivalent) don't support 16x natively but have some spare 1x PCI-e connections that can be re-routed.

Performance is almost the same unless cards with shared memory (ie turbocache) are used. In this case the performance drop is heavy. Having a lot of on-board memory does help because it seems (from the benchmarks I've seen) that streaming textures and vertex from the main memory cause a bigger performance drop than on native PCI-e 16x or even AGP.

The only socket 478 board that I'm aware it's using a native PCI-e 16x connection is the Asus P4RD1-MX built around the ATi Xpress 200.

XDanger
05-30-06, 12:33 PM
P4RD1 on dude :) there is one other mobo i found ,also asus ...

XDanger
05-30-06, 12:37 PM
ASUS P4GPL-X - i915PL ,so is this lame like the p4v800d-x ??

XDanger
05-30-06, 12:39 PM
So its best to go for the 512mb 7900gt version on the p4v800d-x then...