X99 PCIe lane switching

[Ruudt]

The MSI X99 motherboards have the best PCIe switching design in the market.
We allow you to use M.2 PCIe x4 Gen3 on every X99 motherboard (up to 3-way SLI/CFX).
Due to our flexible design we have numerous configuration possibilities, which are not all listed in the regular manual.
Since plugging in graphics cards affect M.2/SATAe PCIe availability things can get confusing.

To inform you what is possible I made the following switching diagrams, I hope this helps:

 

[TZBC]

Wow, it helps me solve the mystery.
Awesome!
Thank you 

 

[m.letcher]

Very helpful. Thanks. I just posted in the Graphics section about getting these choices configured in the BIOS. I'm hooking up a 2nd graphic card (nv-750 in PCI1, and nv-650 in PCI3). I have a the first option (x99s SLI Plus with 28 channels ie a 6-core Haswell). I'd like to configure the lanes as 16x8x4, but it is not at all clear which options in the BIOS would do this. If not, I guess it would be an 8x8x8+4 combo which might be OK. Sounds like I should look more at the Gen3 options in the BIOS. All the BIOS PCI options are set to 'auto', so I presumed it would autodetect the cards and self-configure, but it doesn't appear to be doing so. I don't see the 650 in my Win devices, and suspect it's getting locked out since there aren't 32 lanes available for a default 16x16 setup. Any suggestions?

 

[m.letcher]

After looking into this a bit more, I'll try setting PC1 (750) to Gen3 and PCI3 (650) to Gen2 tomorrow. I think some clouds are parting.

 

[Cdb8457]

OK, I have the i7 5930k with the x99s sli plus. Which lanes would I use for SLI evga 980s?

 

[badboy2k]

OK, I have the i7 5930k with the x99s sli plus. Which lanes would I use for SLI evga 980s?

depends on the type of SLI as there are 3 types!

if its 2 way its slots E1 and E3 will be X16 X16
if its 3 way its slots E1 - E3 and E5 for X8, X16, X8
if its 4 way its E1, E3, E5 and E7 for X8, X8, X8, X8

 

[Cdb8457]

I have mine at E1 and E3. That makes them x16 and x16..... They are almost touching. Would it be back to move the bottom one down to E5 which is x8....How much of a difference to there?

 

[Nichrome]

I have mine at E1 and E3. That makes them x16 and x16..... They are almost touching. Would it be back to move the bottom one down to E5 which is x8....How much of a difference to there?

Hi

According to what I find online, it's about 1-5% performance loss. Try it out on Valley Benchmark Extreme HD preset, and see the differences.

 

[badboy2k]

I have mine at E1 and E3. That makes them x16 and x16..... They are almost touching. Would it be back to move the bottom one down to E5 which is x8....How much of a difference to there?

if you did that both would drop to X8 - X8 as it would switch to 3 way mode so E1 would switch to X8 too as well as E5!

 

[thecrazyscotsman1976]

Ello all..noob and learning..so may have a lame question as im learning and tryin tounderstand. If i have the 5960x , sm951 256gb in m.2 slot as boot drive and 2 msi gtx 980 cards in slots one and four with the sli cable to the outter leftside of the cards,is this all proper and what should i change for switches? Lanes? How do i switch these lanes?..Am not understanding as im still learning. many many thanx if someone can help me out.

 

[badboy2k]

your CPU is a 40 lane CPU! your 2 GTX980's are using 16 lanes each so 32 lanes there so even if your M.2 is using lanes too on the cpu thats a maximum of 4 more so 36 lanes used!

PCI-E lane allocations are automatic so you do nothing!

 

[thecrazyscotsman1976]

Oh mint. Thanks for the reply m8.. think its all good.. now to get the sm951 in m.2 slot  to show up in bios..its all booting etc and read write speeds are 1900 or so and i believes 1200..my score is around top end of 1800s..it shows in windows but not in bios system info section.. i dunno why. Ill have to post a thread and reach out to the community i guess. Again thank ya for yer answer..cheers

 

[dragonguard]

I have:

MSI X99A Gaming 9 ACK
MSI GTX 980 Ti Gaming 6G
Intel 5820k
M.2 Samsung drive with x4 link

Due to the CPU cooler, the first PCIe slot is blocked and I have to use the lower ones.
I put the GPU in slot 3 now as it has the most space there, however it's only using an x8 link according to various software tools.

I assume it is not possible to get a full x16 link if a single GPU setup isn't sitting in the very first PCIe slot?

Thank you.

 

[badboy2k]

I have: MSI X99A Gaming 9 ACK MSI GTX 980 Ti Gaming 6G Intel 5820k M.2 Samsung drive with x4 link Due to the CPU cooler, the first PCIe slot is blocked and I have to use the lower ones. I put the GPU in slot 3 now as it has the most space there, however it's only using an x8 link according to various software tools. I assume it is not possible to get a full x16 link if a single GPU setup isn't sitting in the very first PCIe slot? Thank you.

its still possible! Move the card to the slot just above the M.2 Connector as that is also wired for x16 operation so no its not just the top slot! (the lanes are wired the same as the X99S Gaming 9 ACK) the one marked bellow is also x16 capable!
[attachthumb=1]

 

[dragonguard]

Hello and thank you for your reply. According to the picture, this only applies to CPUs with 40 lanes, or am I wrong?
I'm using the 5820k in my build (28 lanes)

 

[badboy2k]

yeah true! guess your stuck then!

 

[drwhimsy13]

running a 5930K with 40 lanes and MSI GTX 970  twin frozr plugged into an MSI 99A board PCIe # 1 and #3, the card on # 1 is heating to 85-91 Celsius under load, since I want a 16x16 lanes, and I want to OC the VGA how do I solve the cooling problem? IF I move to #1 and # 4 I am 8x8, so with all this flexibility what is my best config ??

 

[flobelix]

What X99A board?

 

[drwhimsy13]

What X99A board?

running X99(S) A Gaming 7

 

[flobelix]

There is about nothing you can do if wanting x16/x16. The only option for x16/x16 is using the cards in E1 and E3. With just one slot of space between them there is simply no space to "breathe". The card in E1 heats up the card in E3 and in addition sucks in the hot air from the card in E3. Because of the small gap between them even a sidepanel fan won't help. The lane arrangement is predefined and depends on slot population. So moving the card to E5 instead of E3 will switch the slots to x8/x8 and nothing can change that. Personally I would go for this option as the performace difference because of the lane limitation will not be noticeable. But since lower temps mean higher boost clockrates and no downclocking you might even see a performance increase when the cards woN't heat up each other and can suck in cooler air.