question for the GPU gurus: how important is having x16 lanes for GPU crunching?

[bmwr606]

looking to buy another pc, dedicated cruncher, so multiple gpu's

looking at motherboards, getting 3 or 4 gen2x16 slots that will all run at x16 means a very expensive mb

however, if x8 or x4 is not a bottleneck for crunching, then i can spend less on the mb and more on the GPUs!

thanks

[Maxwell]

Depends on how big the cards you are planning to buy are. In my rig, an x8 slot seems to be insufficient to display wallpaper and crunch with a 5970.

What flavor of cards are you leaning towards?

[DrPop]

EDIT: I should say this is in my experience, relating to my own rigs or anything I can read on the 'net about this topic:

With all due respect, I'm not sure exactly what the post above mine is referring to. You would be hard pressed to saturate even a 4x PCI-e lane slot when crunching with current GPUs. Let alone an 8x or 16x lane slot! Maybe in the distant future the GPUs will get so powerful that they will need a faster data pipe for data I/O when crunching, but currently, the time spent in data transfer is actually a very little part of the equation. Most of the time, the GPU is crunching the data it was given.
Realize, this "crunching" we do is a very different scenario for the mobo/GPU I/O path than say, playing a high end graphics game like Crysis at 60FPS, where the GPU "needs" 16x speed to transfer data in real time.

[Maxwell]

With all due respect, I'm not sure what the post above mine is referring to.
My 2x5970 rig has an x8 and an x16 slot. Cards will not work, except in crossfire. My only point is that if this is going to be super-duper top of the line cards, there may be issues...

[DrPop]

My 2x5970 rig has an x8 and an x16 slot...there may be issues...

Ah, OK, I see what you're getting at, then. I guess the answer is, "it depends on the exact cards in the setup."

So...I think we can safely say that for normal use GPUs (the 5970 is a special scenario, because there are 2 GPUs on the card, so Maxwell is running 4GPUs in his rig out of 2 PCI-e slots!)...I don't think you'll have much problem with a more usual setup.

But, he is correct - please let us know the model(s) of motherboards and GPUs you're looking at and we can give a much better and more accurate answer.

[trigggl]

Let me hijack this thread temporarily. I seem to remember there being a hack where you could modify a PCI-e card to fit into a 1xPCIe slot. Or was that a different speed slot? The reason I ask is that this Dell does have one 1xPCIe slot and I have an nvidia card that will just barely crunch, that I could put to work possibly. Also, my mom just gave me a dremel tool. >:)

[DrPop]

Yes! You can do this mod by cutting or even melting (:confused::p) the end of the 1x pci-e slot and then inserting the card.

This is possible because the power and bus connectors are always on the 1x end. The longer slots 4x, 8x, 16x, just have more data bandwidth. The only caveat, of course, is that the GPU will transmit and receive data at pci-e 1x speed. Which, for a slower card, would not be any problem at all.

[John P. Myers]

I have my GTX 460 in a PCIe x1 slot. It works fine. A 5970 should as well, but since Max's aren't, i'm betting it's an issue caused by something else. An X1 slot is still 500MB/s bandwidth, which is far more than is needed for a cruncher. I have a 9500GT in a PCI slot (only 133MB/s bandwidth) running all video output from my comp at 1920x1080p res, if that's an adequate example for you :)

So yeah, for crunching, you'll notice no loss at all by going with x16 slots that only use x8 bandwidth. In fact, even in gaming, it was shown there's only a 2% frame rate loss by using 2 GTX 480s in SLI, with one on a x8 slot. And that's gaming. Crunching only requires about 20kB bandwidth, for most projects. Hell, get a mobo with x16 slots that run at x4 if it'll save you money. Won't hurt a thing.

[Zytozux]

Keep in mind that pci-e 3.0 motherboards are suppose to start coming out this year. However, since the only new feature I've seen about them is that it doubles the data transfer rate, it won't have any effect on crunching.

[Maxwell]

Let me hijack this thread temporarily. I seem to remember there being a hack where you could modify a PCI-e card to fit into a 1xPCIe slot. Or was that a different speed slot? The reason I ask is that this Dell does have one 1xPCIe slot and I have an nvidia card that will just barely crunch, that I could put to work possibly. Also, my mom just gave me a dremel tool. >:)
Crunch3r posted the original one you're talking about. If you ask him, he may be willing to share again.

[Maxwell]

A 5970 should as well, but since Max's aren't, i'm betting it's an issue caused by something else.
Farscape (on TM) ran into this issue, too. It's a known, but very uncommon issue. Crossfire solved it, so I didn't have to buy a new mobo. But it's good to keep in mind...

[trigggl]

Crunch3r posted the original one you're talking about. If you ask him, he may be willing to share again.

I seem to recall him cutting the card instead. Now that I think about it, perhaps I could just use the slow one for video so the 9800 can do it's thing without slowing down my video.

[John P. Myers]

Let me hijack this thread temporarily. I seem to remember there being a hack where you could modify a PCI-e card to fit into a 1xPCIe slot. Or was that a different speed slot? The reason I ask is that this Dell does have one 1xPCIe slot and I have an nvidia card that will just barely crunch, that I could put to work possibly. Also, my mom just gave me a dremel tool. >:)

There's a better way, that'll allow you to resell your GPU for a future upgrade. What i did was i got a PCIe x1 Riser Cable. Was only about $8. I drilled the end out of that with my Dremel and just plugged the card into it. Works beautifully

[trigggl]

There's a better way, that'll allow you to resell your GPU for a future upgrade. What i did was i got a PCIe x1 Riser Cable. Was only about $8. I drilled the end out of that with my Dremel and just plugged the card into it. Works beautifully
It's an 8300. I can't give it away. Good info for the future, though. You can never have too many adapters. They have them at NewEgg?

[bmwr606]

i was planning on 3 ea nvidia 570 gpus and no decision yet on cpu/mb

so far the plan is
3 ea nvidia 570 gpu
1 ea big gold power supply
1 ea new case, either haf x or azza hurrican 2000
(will live in an un-airconditioned area)
1 ea old slow dvd rom that i have laying around
1 ea old keyboard and mouse laying around
win7 64 bit
mb and cpu...will see what is "on sale" and supports 3 gpus

i will not be playing any games at all (i have never played a game on a pc) as this will be a dedicated cruncher, probably with the cheapest monitor i can buy

from what i am hearing, bandwidth is not a problem at all

thanks guys

[Fire$torm]

Crunch3r posted the original one you're talking about. If you ask him, he may be willing to share again.

Are you sure? I seem to recall it was JPM that posted modding a 1x slot for 16x cards. If I remember rightly, he posted that shortly after first signing onto the old MB.

[John P. Myers]

Are you sure? I seem to recall it was JPM that posted modding a 1x slot for 16x cards. If I remember rightly, he posted that shortly after first signing onto the old MB.

I posted about modding the slot. Crunch3r posted about modding the actual card.

I think...

[trigggl]

i was planning on 3 ea nvidia 570 gpus and no decision yet on cpu/mb

so far the plan is
3 ea nvidia 570 gpu
1 ea big gold power supply
1 ea new case, either haf x or azza hurrican 2000
(will live in an un-airconditioned area)
Un-airconditioned?
The mother of all case fans (http://www.newegg.com/Product/Product.aspx?Item=N82E16811999612)


1 ea old slow dvd rom that i have laying around
1 ea old keyboard and mouse laying around
win7 64 bit
mb and cpu...will see what is "on sale" and supports 3 gpus

It sounds like a good plan, though obviously I wouldn't be paying for the OS.

[STMahlberg]

i was planning on 3 ea nvidia 570 gpus and no decision yet on cpu/mb ...

Here is a motherboard you might want to look at...

MSI 890FXA-GD70 AM3 (http://www.newegg.com/Product/Product.aspx?Item=N82E16813130274&cm_re=msi_890fxa-gd70-_-13-130-274-_-Product)

I have one in my new rig and I think it's a great board. The really nice thing about it is that it has plenty of room to mount (3) GPU's. See here (http://setiusa.free-dc.org/vbforum/showthread.php?200-Maxwell-Spanker-vs.-Silver-Hammer-vs.-Annihilatrix-pt.-2&p=5887&viewfull=1#post5887).

[STMahlberg]

Un-airconditioned?
The mother of all case fans (http://www.newegg.com/Product/Product.aspx?Item=N82E16811999612)

This also doubles as a hovercraft so you can ride it to work. ;)

http://img811.imageshack.us/img811/7272/fanpc3.jpg (http://www.gearfuse.com/super-cooler-for-pc-is-super-cooler/)

[bmwr606]

thanks for all the replies! :o

the MSI 890FXA-GD70 AM3 AMD MB looks great, i can use sata III 6gbs hd

NEXT QUESTIONS:

the mb supports DDR3 2133 (O.C.) / 1800 (O.C.) / 1600 (O.C.) / 1333 / 1066 ram
for a dedicated cruncher, does faster ram = faster cpu wu completion for a given cpu?
if it does shorten wu completion time, is it worth the extra $ for the high end ram?

does a RAID 0 fast array (2 sata III disks) impact cruching time?

thanks again for the lessons

[STMahlberg]

thanks for all the replies! :o

the MSI 890FXA-GD70 AM3 AMD MB looks great, i can use sata III 6gbs hd

NEXT QUESTIONS:

the mb supports DDR3 2133 (O.C.) / 1800 (O.C.) / 1600 (O.C.) / 1333 / 1066 ram
for a dedicated cruncher, does faster ram = faster cpu wu completion for a given cpu?
if it does shorten wu completion time, is it worth the extra $ for the high end ram?

does a RAID 0 fast array (2 sata III disks) impact cruching time?

thanks again for the lessons

As far as the RAM, from my understanding, it depends on the project. I saw a post somewhere here that faster RAM, and faster HDD's help with certain projects.

If I can find the post again, I'll link it.

[Maxwell]

the mb supports DDR3 2133 (O.C.) / 1800 (O.C.) / 1600 (O.C.) / 1333 / 1066 ram
for a dedicated cruncher, does faster ram = faster cpu wu completion for a given cpu?
if it does shorten wu completion time, is it worth the extra $ for the high end ram?
It can, but not nearly as much as a better CPU would. If it were me, I would go with quality RAM, but by no means spend the $$ for top of the line stuff. Plus, If you buy 1333 RAM, you can overclock it yourself, if you feel like it...

[Fire$torm]

As far as the RAM, from my understanding, it depends on the project. I saw a post somewhere here that faster RAM, and faster HDD's help with certain projects.

If I can find the post again, I'll link it.

A recent post on the subject was Maxwell's "Important Info When Crunching Mersenne@Home (http://setiusa.free-dc.org/vbforum/showthread.php?682-Important-Info-When-Crunching-Mersenne-Home)" thread.

[trigggl]

This also doubles as a hovercraft so you can ride it to work. ;)

http://img811.imageshack.us/img811/7272/fanpc3.jpg (http://www.gearfuse.com/super-cooler-for-pc-is-super-cooler/)

Why not just go with liquid nitrogen?

So, what graphics app was used to create this monstrosity?

[Mike029]

so far the plan is

1 ea new case, either haf x or azza hurrican 2000
(will live in an un-airconditioned area)


I can speak on this case decision. I own the Azza Hurrican 2000 and think it's a great case and got if for a whole lot less than the HAF X. That said the Azza only has 7 expansion slots and the HAF has 9. A fact I missed when making my choice. That alone, IMHO, makes the HAF X superior when looking to build a 3 GPU cruncher.

I'm not unhappy with the Azza, I think it's a great case and if $ is a concern then the Azza is a consideration. You could put together a 3 gpu cruncher in Azza but it will limit your choice of components.