UD3R Shared Bandwidth Question

[cruiselax]

First time system builder here, was about to purchase the GIGABYTE GA-X58A-UD3R when I noticed this:

2 x PCI Express x16 slots, running at x16 (PCIEX16_1/PCIEX16_2) (Note 1)
2 x PCI Express x16 slot, running at x8 (PCIEX8_1/PCIEX8_2) (Note 2)

(Note 1) For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16_1 slot; if you are installing two PCI Express graphics cards, it is recommended that you install them in the PCIEX16_1 and PCIEX16_2 slots.

(Note 2) The PCIEX8_1 and PCIEX8_2 slots share bandwidth with the PCIEX16_1 and PCIEX16_2 slots espectively. When PCIEX8_1 is populated with an expansion card, the PCIEX16_1 slot will operate at up to x8 mode; when PCIEX8_2 is populated with an expansion card, the PC IEX16_2 slot will operate at up to x8 mode.

What does this mean exactly?

I'm planning on crossfiring 2 5850s, does that mean If I decide to put a PCIe soundcard and a wireless card, that the speed of my 5850 crossfire will decrease?

 

[bilbat]

Lets see if putting together the diagrams for the 'memory tutorials' is making me any better at this[:bilbat:8]

Two 'color-coded' diagrams - the board layout:

and - the system block diagram:

The colors on each diagram 'match' the slots to their physical counterparts in the block diagram...

The reason the x16 slots are shown with the 'ever important' "OR" is that you have two 16 lane actual PCIeX16 ports off the IOH (the X58); each one of those ports can operate as one 16 lane slot, if only a 16 lane card is inserted into the first of its two slots, and nothing is in the other; if anything is plugged into both slots of the pair (pair meaning slots colored alike), they 'degrade' to a maximum of eight lanes each... SO - if you only put the two graphics cards into the first of each pair (i.e., the top slot circled in purple, and labelled PCIEX16_1; and the top slot circled in red, and labeled PCIEX16_2, with nothing in the other red, or other purple, you get two, full, sixteen lane GPUs. It doesn;t matter what you put in the blue PCIeX1 slots - as you can see in the block diagram, they are 'hung off' the southbridge, and thus have no effect on the X16/X8 slots at all!

 

[cruiselax]

Lets see if putting together the diagrams for the 'memory tutorials' is making me any better at this[:bilbat:8]

Two 'color-coded' diagrams - the board layout:

http://img179.imageshack.us/img179/1305/0241s.jpg

and - the system block diagram:

http://img194.imageshack.us/img194/6193/0242hk.jpg

The colors on each diagram 'match' the slots to their physical counterparts in the block diagram...

The reason the x16 slots are shown with the 'ever important' "OR" is that you have two 16 lane actual PCIeX16 ports off the IOH (the X58); each one of those ports can operate as one 16 lane slot, if only a 16 lane card is inserted into the first of its two slots, and nothing is in the other; if anything is plugged into both slots of the pair (pair meaning slots colored alike), they 'degrade' to a maximum of eight lanes each... SO - if you only put the two graphics cards into the first of each pair (i.e., the top slot circled in purple, and labelled PCIEX16_1; and the top slot circled in red, and labeled PCIEX16_2, with nothing in the other red, or other purple, you get two, full, sixteen lane GPUs. It doesn;t matter what you put in the blue PCIeX1 slots - as you can see in the block diagram, they are 'hung off' the southbridge, and thus have no effect on the X16/X8 slots at all!

Wow, that was extremely hard to grasp, but I've got a basic idea of it.

So let me recap - now that I can confirm the performance of crossfire will not degrade with me putting something in the PCIex1/2 slots, does it mean I can also infer that putting something in the PCIex8_1/2 WILL degrade it since it is "connected"?

 

[bilbat]

You have it! If you have a sixteen lane card in PCIEX16_1, and you put anything in PCIEX8_1, even just a single lane card, the 'sixteener' 'degrades' to eight lanes, and the 'added' card will 'negotiate' what it needs (up to eight - no more!) at POST...

 

[fadymahfouz]

Okay, Instead of opening a new thread.

I have the same motherboard, with two HD5850 in crossfire and GT240 for physX.

The cards runs @ 16X for the first HD5850, and @ 8X for both second HD5850 and the GT240.

Im planing on adding Asus Xonar to the second PCI-E 1X slot, what would be the configuration then ?? well be anymore degrade to the slots??

 

[bilbat]

Jeezze! I'm amazed it'll work at all - never suspected you could do PysX while running ATI video - are you sure it's actually doing something? How in the world do the drivers manage to 'get along'? (I have a serious reson for asking - thinking about a CUDA card, but don't want to switch to having a couple small nuclear power stations worth of cooling [GTX-480s] in my box...)

You won't see any further 'degradation' from using either of the PCIex1 slots (in blue in the diagrams) - they're on a seperate PCIe bus... In any case, I'm pretty sure a 5850 won't come anywhere near 'saturating' even a x8 PCIe - the xfer rates are not high enough so x8 or x16 really doesn't matter to you...

 

[roonj]

257.15
While this may not be the reason the thread was started, Nvidia somehow put out a driver for one their new cards and someone noticed the code to block functionality with ATI had been left out. It's version 257.15 and a follow up with Nvidia rep stated the release was a beta and the code omission was an accident.
There was additional hype that the release was intended to allow the marriage of both cards with Nvidia hoping they might be able to sell something.
By the way it does work in Windows 7 but not in vista due to version 1.1 instead of 1.0 of the (Wvmd?) memory manager.

 

[bilbat]

Exquisite! I better 'glom onto' a copy of the driver before nVidia hunts 'em all down and kills 'em! WD released a 'patcher' that disabled deep recovery cycling, turning Caviar Blacks, at a hundred dollars, effectively into RAIDable RE3's, at a hundred-fifty - realized their 'mistake', and effectively scoured it off the web...

 

[fadymahfouz]

^^^ nVidia has already pulled the old drivers, but you can found them on techPowerUp For Example.

Also there's a lot of hacked drivers and install methods, but this driver is less complicated, only thing you've to do is to extend the monitor.

 

[bilbat]

Thanks - in storage, already [:jaydeejohn:3] Now I gotta find somewhere to 'borrow' a Tesla from...

 

[devt333]

bilbat, not sure what you mean by this. 5850 doesn't have enough bandwidth to saturate 16 lanes? How do you calculate that? I need a lesson.

 

[bilbat]

I'm just going by comparison reviews - nobody publishes 'hard' info on anything, anymore... If my 'survey' is correct, very, very little actually available will actually saturate a x8; my understanding is that for ATIs, it's the 'twin' (5970), and likely the 2G 5870s, more there by virtue of the 'width' of the 6 monitor setup, than of raw GPU speed... I'm pretty sure, but not 100% positive, that a 5850 is just below the threshold - if it isn't, it's so 'close to the cusp' that the actual difference between a x16 and x8 won't likely be visible to the eye. For the nVidias, it's the 'twin' (GTX-295) also, and the new GTX-480 - I haven't paid enough attention to the nVidia reviews to see 'which side of the cusp' the 470s fall on...

The raw speed of PCIe is pretty staggering: a lane is good for 5Gb/s; but, like most 'signalling schemes', you physically 'move' ten bits for every eight of information, so an eight-lane channel gives you 40Gb/s 'raw', for 4GB/s 'real' transfer rate... That's a shitload of data streaming! Another thing that people usually neglect when considering 'what they need' is that, if you're crossfiring/SLIing, you're moving a substantial amount of data off the PCIe bus, to the 'private', proprietary bus...

Tom's here does some of the best 'real world' reviewing in the business; they aren't cowed by 'synthetic benchmarking scores' - they typically 'wanna see whatshe'lldo in this machine; in your machine!

 

[devt333]

So, now on the video card side, how do we figure out what does it output?

Say, 5850 has a 2560 x 1600 resolution, so that 60 times a second gives us 4.096 megapixel x 60 = 245.76 megapixel. How do they represent a pixel state? 1 byte, 2 bytes? Address in it or synchronized? Not sure. Say, it's 1 byte, so then 245.76 x 8 = 1966.08 that's almost 2 Gb per second. Now accounting for error correction code backwards 1966.08 x 10 / 8 = 2457.6 Mb we got to 2.5 Gb, and that is depending on how do we go from Mb to Gb the decimal or the binary way. If this is correct, than @ 60Hz, the 5850 takes a paltry 2.5 Gb of 40 Gb raw bandwidth that 8 lanes can provide?

 

[bilbat]

No, no - that's the output stream across your DVI/HDMI/DP what-have-you... What's going in is an intermediate geometric descriptor language that's translated by the driver package, and 'understood' by the VidCard BIOS/firmware and the actual GPU array - tessellates, boundary sets, half-dozen kinds of z-order structures - all gets 'whacked together' in some frame buffer structures, and out it goes to make the pretty picture:

 

[devt333]

Oops. That's right, what was I talking about? In other words what goes on on those lanes is the communication between say, a game and the video card rendering it. Which means, that it has to be way, way, way less information that the output that I have so rudely tried to insert into the picture. Holy Cow! That means I have 4 vidoe slots, and not only two, as I was simply not even counting the two 8 bit lanes.

Now, I wish I could take that hard drive OFF!