• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

4 questinos about the P55 chipset

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

Ramon Zarat

New Member
Joined
Oct 12, 2009
Hi.

I plan to upgrade my PC to a Giga-byte P55-UD3R /I5 750/4GB (2 X 2GB) G.Skill F3-12800CL7D-4GBRH 7-7-7-7-21 @ 1.65V/ATI 5850/PC power & Cooling 610

Quality, fast and cheap; just the way I like it! Those G.Skill modules are the tightest AND lowest voltage I could find and they are cheap. (If you have a better suggestion...)

Won't do any crossfire, but could add a cheaper Juniper 5700 series video card for dedicated A.I., physics or faster OpenCL, DirectCompute.



I have 3 questions for you guys about P55 chipset that could change my mind on my choice of motherboard and/or video card:

The 2 X physical 16X slot can have one the the following 2 electrical configuration:

1- 2 X 8X (8X + 8X) or 1 X 16X
2- 1 X 16X and 1 X 4X

QUESTION 1: For config 1, when you choose to have only 1 slot @ 16X, what happen with the second 16X physical slot? It's just disabled?

For config 2, the 4X electrical is provided by the P55 PCIe 2.0 lanes. The only thing is the data has to go through the 2GB/s QPI link already shared with everything else (USB, SATA, Ethernet). See Intel diagram:

p55_diagram.gif


QUESTION 2: Is the 2GB/s QPI link use 4 of the 8 lanes of the P55? Unless the link is not PCIe at all? I try to understand why nearly all P55 motherboard offer so few PCIe slots. On paper you have 16X from the CPU and 8X from the P55. In theory, you could have:

1 X 16X and 1 X 8X or
1 X 16X and 2 X 4X or
1 X 16X, 1 X 4X and 4 X 1X

I think the last one would be the most interesting. You cloud have a 5850X2 plus a 4X RAID controller or a dedicated physics card plus 4 other 1X PCIe add-on card such has a second Ethernet controller, an Asus Xonar sound card, a video capture card and still have 1 PCIe slot left!

QUESTION3: Is there any P55 motherboard that have this 1 X 16X, 1 X 4X and 4 X 1X configuration? I just wish Giga-byte could do a P55-UD3R but with this PCIe configuration!

QUESTION 4: In the diagram, you can see the 16 lanes of the CPU having 16GB/s of bandwidth or 1GB/s per lane. That would mean PCIe Version 3 as version 2 is only 500GB/s per lane. Is my assertion right? If so, then an ATI 5850X2 could be a fantastic choice, if ATI would do a 5850X2 PCIe Version 3...


Ramon Zarat
 
QUESTION 1: For config 1, when you choose to have only 1 slot @ 16X, what happen with the second 16X physical slot? It's just disabled?
Not disabled per se, just not used.
QUESTION 2: Is the 2GB/s QPI link use 4 of the 8 lanes of the P55? Unless the link is not PCIe at all? I try to understand why nearly all P55 motherboard offer so few PCIe slots. On paper you have 16X from the CPU and 8X from the P55. In theory, you could have:

1 X 16X and 1 X 8X or
1 X 16X and 2 X 4X or
1 X 16X, 1 X 4X and 4 X 1X

I think the last one would be the most interesting. You cloud have a 5850X2 plus a 4X RAID controller or a dedicated physics card plus 4 other 1X PCIe add-on card such has a second Ethernet controller, an Asus Xonar sound card, a video capture card and still have 1 PCIe slot left!
Manufacturers wouldn't ever give the option of an 8x port plus others. It would be a tech support nightmare. There could be quite a few people who don't understand their options trying to run a GPU in the 8x port and, say, a sound card in the 1x then calling asking why their setup won't work.
QUESTION3: Is there any P55 motherboard that have this 1 X 16X, 1 X 4X and 4 X 1X configuration? I just wish Giga-byte could do a P55-UD3R but with this PCIe configuration!
Not to my knowledge. The market segment for people who would make it worth the time to manufacture them is likely rather small.
QUESTION 4: In the diagram, you can see the 16 lanes of the CPU having 16GB/s of bandwidth or 1GB/s per lane. That would mean PCIe Version 3 as version 2 is only 500GB/s per lane. Is my assertion right? If so, then an ATI 5850X2 could be a fantastic choice, if ATI would do a 5850X2 PCIe Version 3...
Can't touch that one. The bandwidth may be there, but there are other things involved in PCIe 3.0 than just that. Perhaps they designed the chip with PCIe 3.0 specifications but aren't saying it b/c it's not out yet? Just a random guess...no idea if that's true or not.
 
your forgetting PCIE is bi-directional so it is 16GB/s total. that would mean 500MB/s each way....
http://en.wikipedia.org/wiki/PCI_Express

GPUs starting with or around the 8800's have just started to use more then x8 bandwidth. a X2 GPU is going to be more then fine in a PCIE 2.0 16x slot.
 
You can only have 16 lanes of bandwidth and that is from the CPU. The P55 chipset doesn't provide bandwidth for graphic cards but only for Pci express X1 (as you can see in the diagram). I'm pretty sure this is true. Even if it was true, that means the CPU will have to communicate through the slower-than-QPI "DMI" which will probably slow things down. So it's better if the P55 PCH does it's own job and leave GFX to the CPU.

The only configurations you can run is

X16

or

X8 X8.

If you going to go for 3 way SLI or crossfire don't go for P55. At X8 you may not notice a difference but at X4 you certainly will.

The answer to the first question is yes, the other slot will simply be disabled.
 
The only configurations you can run is

X16

or

X8 X8.

If you going to go for 3 way SLI or crossfire don't go for P55. At X8 you may not notice a difference but at X4 you certainly will.
Just as a caveat, with the NF200 chip, you gain the ability to run Tri-SLI / TriFire. So, depending on which board you decide on, there is the potential for x8 + x8 + x8.
 
I was just asking what happen to the second 16K slot on a board that can do either 1X16X or 2X8X when running in 1X16X mode. Now I know: it's disabled, so I wont be able to put a RAID controller in there.

I don't want to put 2 video card, never was my intention, only an assumption on your part guys. I might buy a 5850 and eventually sell it and get a 5870X2 or something like that, but always 1 slot. 8X for video is still borderline OK for today, but will require 16X real soon, so 8X on the long term is not an option. I will then choose a board that can do 1 X 16X + 1 X 4X and some 1X slot with 1 or no PCI at all.

Thanks you all,

Ramon
 
The boards with 3 PCI-E on P55 have:

2 PCI-E run from the CPU (16x, 1x or 8x, 8x)

They also have another that is ran from what would be the NB... this works at 4x

So you could have: 8x, 8x, 4x
 
Just as a caveat, with the NF200 chip, you gain the ability to run Tri-SLI / TriFire. So, depending on which board you decide on, there is the potential for x8 + x8 + x8.

Yah I posted about this over at XS.

The CPU has 16 PCIE 2.0 lanes

No one seems to know how the NF200 can communicate with the CPU to get more. DMI bus is only 2GB/s and is already loaded up with plenty of other duties (HDDs, USB, Sound, etherent Etc)

I started a thread over at XS about this and somehow lost my subscription to it :s

Seems the answer was finally posted :)


http://www.xtremesystems.org/forums/showthread.php?t=234618


The NF200 does not add any lanes per se, but relies on the limitations of GPUs to only require 16x pcie lanes on the CPU (at the consequence of added latency), by handling all GPU intercommunication and reporting (not quite correctly) more lanes.


Also interesting to note, is that the NF200 can convince the system that 4x 285s are really 2x 295s :eek: That is not good news for hwbot.
 
Also interesting to note, is that the NF200 can convince the system that 4x 285s are really 2x 295s :eek: That is not good news for hwbot.

o_O :eek:

thanks for the link, i was wondering the samething. thinking it some how uses just the 16x lanes from the cpu to send/get data from. that way the NV200 then feeds three x8 slots that way.. kinda like the X2 or newer 295 comm's between two gpus via the PCIE chipset onboard.
 
i have an interesting little bit to share on this.....i have the evga p55, and i was told to run my 3870x2 in the 16 lane, and my 3870 in the x4 lane. i was told this after requesting help as to why adding the second card in the 8x lane actually took my bench scores down. with 16 and 4 set up, as i was told, the 16 runs at 16 so long as there is nothing in the 8 slot, so by running the second card in the 4 slot, i saw a 5% increase in bench, rather than 10% loss.
 
So you got better results running 2 GPUs at x16 and one GPU at x4 instead of running 1 GPU at x16 and 2 GPUs at x4.

I am shocked and amazed.
 
Back