Asus prime B550M-A motherboard pcie lane configuration

[hmadist]

Hello,

I am using the Asus prime B550m-a motherboard with AMD 5500 cpu and RTX 2060S graphics card. I am now upgrading my storage to include two additional MVMe SSd drives. Hence I am trying to use my graphic cards (pcie4.0 x16) and two NVMe drives (pcie 3.0 x4 and pcie 4.0 x4) in the most optimum way. I need to know how the pcie4.0 and pcie3.0 lanes are shared/configured by my motherboard. I have read the motherboard manuals but did not come across this information.

In my search, I have come to know that some motherboards are designed to directly link the pcie x16 slots to the CPU, while other pcie lanes are shared between the pcie x4, x2, x1 and m.2 slots, RAM, SATA, etc. and some lanes are used by motherboard itself. 

Hence I would really like a technical explanation on the pcie configuration specific to my motherboard, in particular, whether there are dedicated lanes for graphics card, RAM and NVMe, so that I can buy the NVMe drives accordingly.

Many thanks 

[Jiaszzz_ASUS]

Hello @hmadist 

Thank you for reaching out to us.
In general, if the PCIe lanes are shared, the user manual will indicate this with a section titled "Connectors with shared bandwidth." For example, you can find this mentioned on page xv of the ROG MAXIMUS Z790 DARK HERO manual.
However, since the PRIME B550M-A manual does not mention this, it indicates that there is no PCIe lane sharing.
Additionally, if you need to make changes to specific slots, such as PCIEX16_1 Mode or M.2_1 Link Mode in the BIOS, you can refer to the PRIME B550M-A BIOS manual for the relevant instructions.

Thank you.

[hmadist]

i came across this from Tom’s hardware B550 announcement (https://www.tomshardware.com/news/amd-b550-chipset-specifications-motherboard-specs,40467.html) : 

“the B550 chipset looks like it will retain the same configuration as past AMD chipsets, which are four PCIe 3.0 lanes . While we're on the topic of PCIe lanes, the B550 chipset brings a couple of interesting improvements. As we already know, the X570 chipset delivers up to 16 general-purpose PCIe 4.0 lanes for motherboard vendors to distribute among other devices. The B550 chipset seemingly supplies four PCIe 3.0 lanes and eight PCIe 2.0 lanes for the same purpose”

I would really like someone from Asus to confirm this PCIe configuration for the prime B550m-a. 

[Jiaszzz_ASUS]

Hello @hmadist 

Thank you for your response and update.
According to the PRIME B550M-A user manual, the specifications for the relevant slots are shown in the image below:

Referring back to the inquiry mentioned in your original post, if you need to purchase an M.2 SSD, you can consider configurations with PCIe 4.0 x4 or PCIe 3.0 x4 specifications.

Thank you.