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pci express - present benefits?

Last response: in Graphics & Displays
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February 6, 2006 9:15:16 PM

ill be upgrading soon but a little confused. to see the benefits of 16x pci-e, you need:

1)compatable motherboard
2)compatable CPU
3)compatable graphics card
4)compatable games

the O.S. - windows website clearly states xp is fully compatable with 16x pci-e (although when i hear VISTA will have "native" support for pci-e i wonder what that means).

the only bottleneck as far as i know right now are the games, which do not support it currently (except fear i think) - but wait... nvidia has SLI hacks for specific games that apparently force 16x pci-e (with SLI). i dont give a dam about SLI, and dont plan to upgrade to it, but can this not work for single-cards? it would be nice to actually see a present benefit from all these upgrades.
a b U Graphics card
February 6, 2006 11:23:01 PM

Benefits are price and availabilty. The AGP versions of the same cards are just as fast (if clocked the same), but cost more now than the PCI-e versions. And even the top APG cards, X850XTpe and GF7800GS, don't matche the performance of any of the PCI-e X1900, X1800, and GF7 series cards.

If your current system still games well for you, keep it. But When it comes the time to build a new gaming system, don't even think about going AGP.
February 6, 2006 11:45:14 PM

theres no question ill go pci express.. i was just wondering if present games can benefit from the increased bandwidth (they do not now).
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February 7, 2006 3:30:50 AM

Actually they do. Just take a look at the new AGP version of the 7800GS that Anandtech.com benched last week.

http://www.anandtech.com/video/showdoc.aspx?i=2686

The card is clearly bottlenecked by the inferior AGP bus. It's a good 20% slower than the 7800GT. The only real difference between the GS and GT is this:

GS has 1 less vertex shader (GT has 7)
GS has 4 less pixel shaders units (GT has 20)
GS has AGP interface (GT is PCI-e)

-mpjesse
a b U Graphics card
February 7, 2006 10:38:49 AM

Quote:
The card is clearly bottlenecked by the inferior AGP bus.

I don't at all agree with that comment. OC'ing the 7800GS yields a huge performance increase over stock speeds. Doesn't sound like an Inferior AGP bus is bottlenecking the 7800GS. Also, A X850XTpe is faster than a 7800GS and it performs equal in PCI-e and AGP. I just did some testing of my 6800U for another thread, and found even AGP 4X providing less than 0.5 fps difference (in Farcry at least, plan on doing fear also) than a 6800U at 8X AGP.

I'd like to see the data if NV or ATI has done tesing on this and found a saturated AGP bus makes them not make faster AGP cards. But I'm convinced even the real 7800GT and X1800XL wouldn't saturate the AGP bus in todays games. If they decided from a financial standpoint to release these cards in AGP, I think we'd see identical performance to the pci-e cards.
February 7, 2006 11:19:44 AM

yeah but for the price of 7800 GS, you can get a pci-e mobo and 7800 GT.
a b U Graphics card
February 7, 2006 12:56:04 PM

Quote:
yeah but for the price of 7800 GS, you can get a pci-e mobo and 7800 GT.

While I totally agree, why did you reply to me with that info? I'm not saying buy a 7800GS. Far from it; it's a lousy way to spend $350, hence the pricing and availability comment. But I don't think the AGP bus is holding the 7800GS back at all, nor do I think it would have held back a 20 pipe 7800GT if NV had decided to really do something nice for the "luddites" :wink: .

Edit: Matter of fact, I wouldn't even wager my lunch money that a X1900XTX could saturate the AGP bus playing Fear, COD2, etc. Are there games pushing enough poly's to saturate AGP 8X, and is there hardware yet that could be capable of running such textures at the resolution and setting people would game at? Beats me. Grape, Crash, anyone know?
February 7, 2006 12:59:13 PM

Quote:

The card is clearly bottlenecked by the inferior AGP bus. It's a good 20% slower than the 7800GT. The only real difference between the GS and GT is this:
GS has 1 less vertex shader (GT has 7)
GS has 4 less pixel shaders units (GT has 20)
GS has AGP interface (GT is PCI-e)
-mpjesse


Uh, I wouldn't say that AGP is 'clearly bottlenecking' that card when you list all of the other differences that could easily account for that 20% difference.
a b U Graphics card
February 7, 2006 1:39:48 PM

"i was just wondering if present games can benefit from the increased bandwidth (they do not now).
"

The bandwidth itself available over the interface (AGP 4x/8x vs. PCIe 8x/16x/16x2) is not an issue yet, but, as all the top performing cards are available only in PCIe, you needn't ever worry about bandwidth issues at all.

The performance increases are not really coming by virtue of the PCIe interface itself, but it just so happens all the faster, loaded cards happen to be on that interface.

We can't really say the AGP interface is the cause/bottleneck of the 7800GS' dismal performance relative to a normal 7800GT; if it was, then overclocking the GS would not yield appreciable performance increases, when it clearly does.
February 7, 2006 2:10:33 PM

Quote:
The card is clearly bottlenecked by the inferior AGP bus.


That is absolutely flawed logic. 4 less pixel pipelines and one less vertex shader would easily account for the 20% drop in performance. Not to mention, the 7800GS has far fewer ROPs than the GT.

When you look at other cards with IDENTICAL specs that go between AGP & PCIe with NO performance difference, this is a very, very strange conclusion to come up with...
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