ASUS X99-WS/IPMI bifurcate x8 slot/s to x4x4

Hi, I have tried following the guides posted but I am struggling a fair bit with the process.

I would like to split my top slot from x8 to x4x4.

IOU2 (IIO PCIe Port 1) seems to refer to this slot but am I right in saying any changes made will also apply to my other x8 slots - 4 and 5?

Expansion slots.jpg

Lane config.jpg

I am using a 40 lane CPU.

I would like to leave the two x16 slots (2 and 3) as is.

If slots 1,4 and 5 can all be split from x8 to x4x4 that’d be great.

I did try this myself using AMIBCP but failed to produce a BIOS I could flash using USB flashback.

Newest BIOS for the board - Newest BIOS

The BIOS options are limited, I’m not sure if it’s possible to enable anything which is hidden by default.

Any help would be massively appreciated.


@Blunt - Use HWINFO64 and a single card to test with (can be GFX Card), check the BUS area and see what each slot shows up as being split into. But first, you need mod BIOS with IIO changes, so, I can make you BIOS with 4x4x set on one IIO and or slot at a time
Then you’ll have to flash each one by one and test/look in HWINFO64 and see which one is the slots you want/don’t want. Then once you have it all written down in notes, which to not change to 4x4x then I can make you final BIOS with all except those ones changed to 4x4x.
This will be 4x3=12 BIOS to test, or you can stop at any single BIOS you want and use that, I will only change one slot per IIO per BIOS. There is four IIO, with three slot settings (IOU0-2) in each one, that’s why so many BIOS to test.
Load optimal default after each BIOS flash, this is the only thing I changed (did not change fail-safe, so be sure to start with optimal). Also, all BIOS will have same name and must be kept that way to USB Flashback, so don’t mix things up as you test

I can make you mod BIOS with hidden settings visible, but I don’t think I can make one with this submenu for IIO visible due to where it’s located in BIOS (outside of setup)
You’re can’t already see IntelRCSetup in BIOS, correct? If you can see that, let me know and wait if you want, I can make you mod BIOS where everything you need IS visible inside that area.

For now, here is the BIOS I mentioned above, with one each set to 4x4x per IIO, and per slot in that IIO (may cover more than one slot each, only your testing and inspection in HWINFO64 will let you know)
Ahh, on pause, there is no 4x4x setting only on two IOUx per each IIO, what do you want me to use instead (4x4x8x, or 4x4x4x4x), or do you just want me to make you four BIOS only with single change on each IIO / w/ slot (IOU2) to 4x4x? << Yes this, lets test these four first and see if they work for you, if not we’ll do the others…746099038067357

If you want to play yourself, and be able to USB Flashback, remove BIOS body from capsule with UEFITool (at top in middle, right click AMI Capsule, extract body) Then edit this.
Then open stock .CAP BIOS in hex editor, go to 800h location, open mod BIOS body in second tab of hex editor, select all and copy, go back to stock BIOS .CAP and at 800h, paste your mod BIOS body from 800h to end, then save with USB Flahback name (X99WSI.CAP)
To confirm you did correctly, open mod BIOS in UEFITool, and see that is looks same as stock at top >> AMI Capsule Signed, and then also expand and make sure BIOS body inside capsule looks same as stock generally, expand capsule, and expand Intel Image (just to confirm your paste was OK

If you’ve not used USB Flashback before, with this board and your current USB Sticks, let me know and I will give you some general tips

Dude, you’re an absolute legend thank you :slight_smile:

I’ll get on this tomorrow morning and report back with my findings. I’ll check the bios and let you know what I can and can’t see.

When you said

“there is no 4x4x setting only on two IOUx per each IIO, what do you want me to use instead (4x4x8x, or 4x4x4x4x), or do you just want me to make you four BIOS only with single change on each IIO / w/ slot (IOU2) to 4x4x?”

That sounds right. 4x4x8x and 4x4x4x4 applies to slot 2 and 3 but I’d like to avoid changing these if I can.

Will HWINFO display the full bus breakdown without populating all the slots? I had a ASUS riser which I’ve since returned. I’m going to order the Supermicro AOC-SLG3-2M2 but it’ll maybe take a week or so to get here.

Thanks again

@Blunt - Well thank you!

No, about the 4x4x8x or 4x4x4x4x etc, it’s very confusing, especially if you cannot see all the possible settings, to be able to guess what IIO is what and what IOUx within that IIO is what slot on the board.
This 4x4x8x for example, only applied to a SINGLE slot directly, nothing to do with any of the other slots. This setting example, would bifurcate a single slot to 4x4x8x (so you could use 3xNVME on a single slot)
Each IIO has 3 IOU’s, and each of those can have certain configurations applied to each one, but not all can be applied to the same slots in same ways. If you look at the BIOS in AMIBCP you will see what I mean.
But, if you can see IntelRCSetup section, I will be able to easily make it ALL visible to you, so then you can jump into the massive confusion pool with me

For HWINFO, no, you need to test each slot one by one with some device (GFX card or single NVME), make notes which slot is what. Then test BIOS changes per IIO, and then within each IIO, per IOU and makes notes of all that.
This is MUCH easier if you can see all the settings, so you know what you are changing and can test as you change. So hopefully you can already see IntelRCSetup, because I cannot make that visible for you

Can confirm I can’t see IntelRCSetup in the bios anywhere

Hang with me and I’ll do some testing with the bios and get back you. The board is currently in use in my Unraid server.

Thanks again


Have just finished testing the 4 bios .CAPs.

I wasn’t able to strip the board down to a single card and test on a slot by slot basis, I have all pcie 5 slots populated as I would like them in the server.

Added some screenshots below.…691896364676020

I tested all 4 and didn’t notice any changes after flashing each bios, no split in the bus and no noticeable difference in HWINFO. Each time I loaded optimised defaults as advised. The IIO-2 4x4x bios seemed to cause a few issues with USB but that was my only observation.

The slot/bus order is:

1 - Root Port 3c
2 - Root Port 3a (IOU1)
3 - Root Port 2a (IOU0)
4 - Root Port 2c
5 - Root Port 1 (IOU2)

Looking to split slots 1, 3 and 5 from 8x to 4x4x

Hope this helps for now. Any suggestions, thoughts or anything else I need to check?

Thanks again

@Blunt - Bummer no IntelRCSetup This means only you or I editing settings directly can change stuff there. Thank you for that slot info, maybe I can use it to pick correct slot.
In each BIOS I sent previously, I only change IOU2 (IIO PCIe Port 1) to 4x4x on each (0-3) IIO. For each IIO, there is only IOU0-2 (IIO PCIe Port 1-3) settings, and not all have 4x4x, 2-3 have all the usual expected options (single, all the way through 4x4x4x4x)

From the info above, one of the BIOS I sent you, or more, should have affected #5 (IOU2), since that is what all those BIOS changed (IOU2).
Can you re-test all those BIOS, and confirm for me which gave #5 4x4x? Then, I will keep that set, if you want, and build upon that. Or do you not have a card in your possesion yet that can split 2 NVME’s?
If you do not, then we need to wait until you do, so we can confirm the change or not, otherwise no way to see the split I think. And it’s possible, that some of the slots may split the way you want by default anyway, since all are on Auto.

IN addition to one of the BIOS I sent you before, which one should do IOU2 the way you want. It sounds like you would also need, IIO 0-3, with both IOU0+1 on each set to 4x4x4x4x, or 4x4x8x (there is no 4x4x only option on the rest of the possible slots, only the BIOS you tested above offer that choice)
Ideally, I’m sure what would work best for you is probably some combo of that, or only certain IIO/IOU’s set that way, but without you being able to directly change in BIOS one setting at a tine and test, this is going to be very tough to figure out (because we do not know from above info, what slots are what IIO)
Moving forward, for each test, do you want me to use 4x4x8x or 4x4x4x4x?


Thanks again for your help. I ordered the Supermicro dual riser on Sunday night. Should hopefully arrive this week and I’ll retest each bios with the riser in slot 5

4x4x8x sounds great moving forward. I have a GPU in slot 2 and 4 so as long as I can still run both x8 that’d be great. Happy for the other slots to be split the same way. Having the option of adding another riser or two later would be perfect.


Finally got my riser card :slight_smile: Was shipped from Berlin so it took a while to get here.

Just to confirm - I should load optimum default settings in the bios after each flash?

On first boot after flashing the IIO-0 bios I can see the second nvme drive (Corsair MP510) in the bios but not the first drive (Samsung 970 Pro). When I load optimal defaults then F10 to save and reset, I see ‘you have not made any changes’ followed by a hard reset. Once the board reboots I can see the first Samsung but not the Corsair.
Would it be possible to try each of the four bios with both failsafe and optimal 4x4x? I’m not convinced the optimal settings are being applied as they should be. Unless I’m doing something wrong? :frowning:

Have tried all 4, loading optimised defaults as above for each but I still can’t see any change to the bus in HWINFO.

Hi, sorry to post on an old thread, but did you have any success here? I’ve just got an X99-IPMI and I’m looking to do the same - or at least on one of the slots have the ability to change it to x4/x4/x4/x4…
I’ve got hold of an old bios that has x16 or x8/x8 options in the bios for slot 2 or 3 (as well as Thunderbolt support!) but i’ve never gone into bios editing before so i’m not sure where to start (happy to try though!)

If anyone has any other links or places to look that’d be greatly appreciated :slight_smile:

Thanks in advance