B650D4U vs. B650D4U3
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=108008
Printed Date: 04 Sep 2025 at 6:46pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com
Topic: B650D4U vs. B650D4U3
Posted By: prak32
Subject: B650D4U vs. B650D4U3
Date Posted: 14 May 2025 at 2:58am
What is the big difference between the two AMD motherboards: B650D4U3 vs B650D4U?
Is it basically the PCI slot and the M.2 slot swapping CPU vs. FCH?
Any other differences?
BIOS management software the same (BCM)?
What does the "3" mean?
Also curious why more PCI lanes aren't available to the CPU. Is this a chipset limitation? AM5 socket limitation? CPU limitation?
Thank you,
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Replies:
Posted By: eccential
Date Posted: 15 May 2025 at 7:57pm
Looks like 3 also lost the DisplayPort output.
Ryzen 7000/9000 EPYC 4004/4005 only have 28 PCIe lanes, and 4 of them are used to connect to the chipset (Fusion Controller Hub as it was designated in the AsRockRack page). So ultimately, you get to play around with 24 lanes.
16 + 4 + 4 is all you'll get, and the only difference will be how you arrange them.
You can of course also do 8 + 8 + 4 + 4 or some other arrangement, but you'll never get more than 24 from the CPU on AM5.
I do wonder if there are any boards WITHOUT a chipset (also known as X600), giving you access to all 28 lanes from CPU.
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Posted By: prak32
Date Posted: 15 May 2025 at 11:39pm
You're right. The motherboard variants are shifting the PCI lanes around. Some are direct to CPU, some are going through the chipset. It is my understanding the CPU is the fastest.
For me, I want to run dual M.2 (I mirror my SSD drive). I don't want them running at different speeds either, so I want both drives to have direct CPU access. The other PCI requirement is for my HBA card. The only feature I'm missing is faster LAN/Ethernet, but don't want to give up my need for fast drives.
B650D4U3 (+SATA, -MCIO) or EPYC4000D4U (-SATA, +MCIO) look to be the best choices for me.
Unfortunately neither are in stock. Not sure what's going on with availability (is nobody able to build AMD5 servers right now??) Frustrated.
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