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How much will PCIe 4x affect performance?

Last response: in Graphics & Displays
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October 16, 2007 12:38:19 PM

Basically I'm looking to upgrade my aging Geforce 7600GT AGP to a Geforce 8800GT, when they come out. One thing I wondered about though is that my current motherboard, Asrock 775dual-VSTA, only has a PCIe 4x slot and I just wondered if/how much this would bottleneck something like a 8800GT.

Thanks.

Rig -

Asrock 775dual-VSTA
Core2Duo E6600
Enermax EG365AX 350W PSU
1.5Gb DDR RAM *(soon to be 2Gb DDRII)
500Gb HDD
Geforce 7600GT
October 16, 2007 12:42:21 PM

I heard that it wasn't a big deal, since cards don't use all the bandwidth (that was for x8 though, not sure about x4).
October 16, 2007 12:43:53 PM

most likely it'll just down clock to 4x
a c 143 U Graphics card
October 16, 2007 1:58:04 PM

So, it may work at 1/4 of its capacity (i.e. even fewer fps than the 7600 GT), or it may work at almost full capacity, depending on the game. I think it's time for a new motherboard. Something like GA-P35-DS3L, maybe?

I think you'll need a new PSU too.
October 16, 2007 2:04:30 PM

According to the article, you will definitely need a new motherboard.
The 8800GTS is severely limited by the 4x PCIE. The 8800GT which is rumored to be faster will definitely deliver well under 1/2 its possible performance.

The GPU may be borderline, we will need to see.
The 8800GT is supposed to use less power than the 8800GTS so we will just need to see how much less.
October 16, 2007 2:06:25 PM

Wolfshadw said:
http://www.tomshardware.com/2007/03/27/pci_express_scal...

Read through this.

-Wolf sends


Thanks Wolf. Very useful.

So basically it makes a very big difference. Now my only problem left is to decide whether I should just suck it up, buy the card and put up with the loss in performance, buy a new motherboard, or buy a Radeon X1950 and stick it out with AGP for a little longer...mmm...
October 16, 2007 2:08:51 PM

Thos graphs do however put up some further questions.

Since only the 8800 and the x1900's were used, it could mean one of a few things:

1- The Nvidia cards are affected more than the ATI ones (since we have no data on the 2900's performance at 4x pci-e and also since we dont have any data on how the 7900 cards run at 4x pci-e)

2- It affects new gen high end cards a lot more irrespective of make (since they need more bandwith than can be supplied by a 4x pci-e slot )

Someone needs to take a bigger range of cards and run them through the different slots cause just using a 8800 and a x1900 doesnt seem good enough to me.

I would have liked to see 1900, 1950, 7800, 7900, 8800, and 2900 in there.

October 16, 2007 2:18:14 PM

To put it this way: a 7600GT is probably limited at a AGP4x bandwidth (1067 MB/s) and PCIe 4x runs at 1000 MB/s. Your 8800GT in that interface would be trying to suck a bullfrog through a garden hose. So going from a AGP 8x to a PCIe 4x is a very bad idea. All this information is available on Wikipedia under the title "List of Device Bandwidths".
October 16, 2007 2:21:36 PM

Mmm...looks like I may have to go for the new m/b and psu then if I want to upgrade the gpu. Mmm...this could prove expensive.
a c 143 U Graphics card
October 16, 2007 3:11:11 PM

But it will be a MUCH better machine :) 

Just wondering, does anybody know how big the 8800 GT will be? Will it be as big as the GTX, forcing some people to upgrade their cases too?
October 16, 2007 3:30:37 PM

9 inches long and single slot, that much about it is 100% confirmed lol

(dont flame me again :D  )
!