Question regarding PCIe bifurcation on B850M SLW
Printed From: ASRock.com
Category: Technical Support
Forum Name: AMD Motherboards
Forum Description: Question about ASRock AMD motherboards
URL: https://forum.asrock.com/forum_posts.asp?TID=107781
Printed Date: 05 May 2025 at 8:49pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com
Topic: Question regarding PCIe bifurcation on B850M SLW
Posted By: sr5ttyhrsyha
Subject: Question regarding PCIe bifurcation on B850M SLW
Date Posted: 05 May 2025 at 12:39pm
I'd like to confirm if the B850M SLW ( https://www.asrock.com/mb/AMD/B850M%20Steel%20Legend%20WiFi/index.us.asp#Overview" rel="nofollow - https://www.asrock.com/mb/AMD/B850M%20Steel%20Legend%20WiFi/index.us.asp#Overview ) can have it's PCIe x16 slot bifurcated to x4x4x4x4 in order to allow bifurcation required type adapters (like https://www.amazon.com/GLOTRENDS-PU41-Bifurcation-Function-Motherboard/dp/B0D3XX7PSF" rel="nofollow - https://www.amazon.com/GLOTRENDS-PU41-Bifurcation-Function-Motherboard/dp/B0D3XX7PSF ) to work without a PCIe switch. I would be using a Ryzen 9700x CPU.
Manual here: https://download.asrock.com/Manual/B850M%20Steel%20Legend%20WiFi.pdf" rel="nofollow - https://download.asrock.com/Manual/B850M%20Steel%20Legend%20WiFi.pdf
Sadly, "bifurcation" and "x4x4x4x4" do not show up in a text search.
However there is a section:
>RAID ??Supports RAID 0, RAID 1 and RAID 10 for SATA storage devices
> ??Supports RAID 0, RAID 1 and RAID 10 for M.2 NVMe storage devices*
>* Requires additional M.2 NVMe expansion cards to support RAID 10
That indicates it may exist, but has just been poorly named.
(Note to asrock marketing if you see this, mentioning "bifurcation" and "x4x4x4x4" is a good idea if those are supported. IF they are not supported, explicitly saying so is a good idea to remove doubt)
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Replies:
Posted By: NDRE28
Date Posted: 05 May 2025 at 3:43pm
Hi!
All I can say is that I'm using an X670E Taichi, which has two x16 PCIe slots, and which offers the following bifurcation options (and they do work):
1. x8x8 (top & bottom PCIe slots run in x8 mode).
2. x8x4x4 (bottom PCIe slot runs in x8 mode; top PCIe runs in x4x4 mode).
3. x4x4x4x4 (bottom PCIe runs in x4x4 mode; top PCIe runs in x4x4 mode).
NOTE:
Lanes can be upgraded or downgraded to: Gen5, Gen4, Gen3, Gen2, Gen1, but the lanes number remains the same!
With other words, you can't achieve more PCIe lanes by downgrading from Gen5 to Gen3.
I hope this helps...
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