[Guide] Adding Bifurcation Support to ASUS X79 UEFI BIOS

Sorry for the late reply,
Not knowing what or how many your connecting to you PCIE I recommend either buying a ~300 EUR+ card that does PLX/PFX/PEX lane switching (optional M.2 Key M to PCIe x4 NVMe Adapter cables); or switch platforms to something like amd tr4 threadripper, or x299(cannot do hardware NVME raid).
I have not tried the Above 4G setting. As for the other unlocked BIOS settings it is quite a mine field.

Thanks for your reply anyway.
Could you recommend anything except boards shipped by c-payne.com? 350 EUR for the board, +re-driver cards and SAS cables to get the config out of the pc case… Well, it’s a serious investment ))

Other observations: I can bifurcate x16 slot (third from cpu socket) and it works more or less ok (except for the Tesla K40 that blue-screening periodically in the bifurcated slot but works ok via USB riser in PCI 2.0 x1 slot). However, when I’m trying to bifurcate x8 slot (to the pair of the x4 links) Win 10 shows unrecognized device for the second x4 link and can’t install drivers for anything: tested with several GPU-s, WiFi card, NVME with adapter. Did anyone tried the x8 slot bifurcation with other type of re-driver cards than I’m using - like dual M.2 cards?

I see in the bios the 8x slot has the x4x4 option. Anyone try that slot to use 2 NVMe drives ?

I am thinking about a card like this



@chuckbam Did you end up getting 3 or 4 NVME drives working off this adapter?

the adapter only holds 2 NVME drives. I did not buy it yet

@chuckbam Quote from your link: Supports 4 X 2280 NVMe M. 2, I think the card might have 2 sides with 2 drives each. However 2 of them will probably work in x4x4 bifurcation.

@JackSted ,

Your right holds 4 drives.

@JackSted ,

So there is a electrical issue with 4x4x4x4x on the first two 16x slots but the 4x4x works on the bottom 16x (8x) slot ?

Chenyang Dual 2X NVME M.2 AHCI to PCIE Express 3.0 Gen3 X8 X16 Raid Card VROC Raid0 Hyper Adapter (Only Supports motherboards with Detachable PCI-E Channels)

From reading back to page one, trying to skip through flashing and installing Windows replies,

I have one question. Does the Bifurcation Support to ASUS X79 UEFI BIOS work?

Thank You

@JackSted I’m having a hard time finding the link for your p9x79 bios file, is the file still up?

Asus Bios P9X79-4701-Mod-NVME-SA-Switch.zip (4.6 MB)

I would still like to know if the 4x4x Bifurcation works on the bottom 16x (8x) slot with this bios?

Hey, would you be able to reupload this bios by any chance?

Currently I just have the mod to boot from a nvme drive, however I now need bifurcation due to my lack of ports.

Thank you.

First post updated to add link to the bios.

1 Like

edit: been at it for too long. it’s litterally just +1 on two values in hex of .sct extract; replace, flash, boom; 4G + IOH options

For future Asus X79-Deluxe owners:

Using a bifurcation PCIe x16 to 4x4x4x4 NVMe adapter (mine is made by iocrest: link here), I am currently unable to get bifurcation to resolve the number of installed drives. It will show one fewer than the number of installed drives.

If I install two drives, only a single one shows in BIOS. If I install three then the BIOS will see two. I don’t have enough spare NVMe drives in order to populate all 4 slots and see what happens.


  • i7-4820k
  • GTX 1070 top slot (I believe IOU2 - PCIe x16_1)
  • PCIe x16_2 (full x16; I believe IOU3, enabled as 4x4x4x4 in BIOS) - tested
  • PCIe x16_3 (x4 electrical) - Mellanox Connectx-3 NIC
  • PCIe x16_4 (x8 electrical, IOU1, enabled as 4x4 in BIOS) - tested

BIOS version 4805 BI ALL ME (h/t Deluxe, Lost_N_Bios, Meatwar)

will update/edit this if I can get anything more conclusive for each slot

Update – having borrowed an extra x8 card and populated it with two NVMe drives, I get some weird behavior:

Enabling 4x4x4x4 bifurcation combined with 3 fully-populated drives results in one drive from the x16 card being visible, with one drive visible in the x8 card (with 4x4)

But if I change the cards (so the x8 is in the x16 slot, and vice-versa), then a different drive for each card is visible – the other drive in the x8 card becomes visible, and another drive on the x16 becomes read.

No more than 1 drive per x16 slot is visible, unfortunately. I just can’t get it to work.

It is reported like so in the OP post…
I do believe that it’s a X79 pcie lane limitation, 40 lanes from cpu (Plus 4 extra), but seems that DMI and some other connected devices will use it… if you care to read a bit there’s plenty of discussion here in the comments.
I had a X79 but sold it way before the BIF mod/NVMe or PCIe adapters.
Can’t recall for sure but i think users with X99 had more success, only my opinion only.