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PCIe 1.0 x 8 SLI bottle neck

Last response: in Graphics & Displays
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October 19, 2011 9:12:24 PM

Hello,
I have an old XPS 630i I bought from DELL back in '08. Recently my single GPU kicked the bucket (512 MB GeForce 8800 GT). Well rather than spending all the money on getting a new mobo/CPU/upgrade RAM/Win 7 64-bit to make the most out of being compatable w/ PCIe 2.0+ for all the latest GPU's, I'd like to make the most of everything else that's still working in my old 630i. What I feel many people didn't realize about Dell's, specially made (i.e. they manufactured it) nforce 650i SLI, is that when you're only running a single GPU off of this mobo designed primarily for old SLI cards, it's only running on PCIe 1. x8 and not x16 as so many would expect. Many other mobo's that do run in 2 x 8 mode can switch to make full usage of 1 x 16, including other manufacturers of the nForce 6 series, but this one simply wasn't designed that way. I guess their attitude was "take it or leave it, x 8 is the most lanes you're getting, might as well double it up". My question is, in fear of the obvious x8 bottle neck (remember this isn't PCIe 2.0 this is 1.0!) for a single high performance card, what would be the highest performance SLI cards I could get before the x8 renders it +/- 1%, 5% inefficient due to the bottle neck (I know SLI is only ~1.86 times as powerful as only using one of the same GPUs but I feel since x16 is not compatible with my mobo 2 x 8 is my best performance option). I've spent hours searching this problem, it seems my rig is getting really antiquated since I can't find a simple answer after hours of research to what the best GPU in SLI I can run on 2 x 8 before there's a PCIe bottle neck. Many thanks in advance!!

More about : pcie sli bottle neck

a b U Graphics card
October 20, 2011 4:07:55 AM

Off the top of my head
Just an educated guess
I would think twin GTX 460 768mb would be your best setup
great prices right now
and x8 shouldnt bottleneck them severely
actually your 2008 CPU might be more of a bottleneck problem than the X8 slots
(without knowing your CPU that is just a guess)
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a c 143 U Graphics card
October 20, 2011 2:01:01 PM

king smp said:
Off the top of my head
Just an educated guess
I would think twin GTX 460 768mb would be your best setup
great prices right now
and x8 shouldnt bottleneck them severely
actually your 2008 CPU might be more of a bottleneck problem than the X8 slots
(without knowing your CPU that is just a guess)

He's saying PCIE 1.0 not 2.0
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a b U Graphics card
October 20, 2011 9:27:58 PM

Well it is tricky using 2.1 cards in 1.0 slots
sometimes work sometimes not
definitley would want to update the BIOS first
also maybe go with dual HD 5770s or dual GT 450s (I think board is SLI capable
so dual 450s would work)
even find older 260s and sli them
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October 27, 2011 3:57:56 AM

Thanks for the suggestions/help king smp & ilysaml!

Update: Well, rather than buying 2 cards, I went with just one to make sure my setup could handle it. After checking out some performance charts (hierarchy Nvid cards using 3D Mark http://lifehacker.com/5840839/this-chart-actually-expla...) it's interesting to note the "pulse" that you can see with every new generation. Anyways, I went with a single 1024MB GDDR5 GTX550Ti http://www.geforce.com/Hardware/GPUs/geforce-gtx-550ti/... for a number of reasons. Maybe it was a bad choice for the video card gurus, but so far it's working flawlessly despite having only 2G's of ram on Vista 32! The main reason I chose the 550Ti was because it was a highly rated "budget" card, it has a 6-Pin power connector, it's the low end of the newest generation more/less (so it's made for Direct X11, 3D--which I won't have--among other goodies), it's memory bandwidth is only ~105 GB/sec (EVGA model) (normally a bad thing but I figured I'll be facing bottle neck issues anyways), and it's minimum power requirement is only 400w (really quite an efficient little card). I noticed that while running system performance monitor though, my CPU (only dual core E8400 3.0 GHz 1333FSB, 6MB cache) is often running @ 100% frequency but using only ~60% of the CPU... I take it that's bad news if I was planning on adding a 2nd one to SLI (although I really don't plan on doing that now anyways since I'm happy with single card performance atm for SC2 and will be actively boycotting BF3 for lack of realism--never run out of fuel, doesn't require actual landings reloading/refueling, gauges are not functional, doesn't include a number of things that I feel were necessary to keep dogfights progressing to new levels of difficulty from BF2). King smp I think you were right about the bottle neck likely being my CPU now...The question for me now is, do I return the card for something cheaper that I can SLI, or is it best to leave it for now. Another question I have is what's the best kind of memory for the price for DDR2 800MHz, and is it really worth it beyond 2GB w/ Vista 32-bit (i.e. max is 4 right? but only 2.5 of it is usable? so does that mean add another 2 gigs and you only get a half gig of performance back?) Sorry for that last question, although I'm sure I'm not the only one that doesn't know as much as I should about a 5 year old question... lol Once again, many thanks in advance!!
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a b U Graphics card
October 27, 2011 4:43:05 AM

I think the 550Ti is great choice
in a new build later you can sell or possibly do SLI with another 550Ti

as far as ram
even though Windows has usually 2.5gb of the 4gb
that is available for running apps
but it is using roughly 3.5gb which the 1gb difference is for OS and background apps

You do usually lose about 512mb(.5 gb)
because of the 32bit restriction on memory address space

but with the cost of RAM really chip
it is better to get two matching 1gb sticks IMHO

I dont think you need performance RAM
so I would recommend this budget line of Crucial

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

that is $26 USD with shipping included

you can actually find it cheaper
but I would stick with Gskill,Corsair,Crucial or Kingston

and go with their basic "model"
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October 27, 2011 11:03:47 PM

thanks again king smp!
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a b U Graphics card
October 28, 2011 1:01:10 AM

It all depends how lazy the game designer was when they designed a game. You can reduce bandwidth by requesting data less often eg do more math and share/reuse data i.e. Increase the on-chip storage .

The cards of today can run much better if it wasn't for lazy developers. A efficient gpu workload is not limited by bandwidth. That can be done by having a high ratio of math operations to memory access.

What cpu do you have in that Dell btw?
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October 30, 2011 12:00:13 AM

Best answer selected by right.
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a c 271 U Graphics card
October 30, 2011 12:33:03 AM

This topic has been closed by Mousemonkey
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