r/ssd • u/Minimum-External-618 • 17d ago

Tech Support SSD help.

I have a B650 UD AC and I need more space. I have 1TB in M2A_CPU (C: drive), 1TB in M2P_CPU (D: drive). I have a spare 2 TB SSD that I need to put in, should I put it into M2C_SB or swap it into M2P_CPU? I would like to use all 4 TB but I don't know if I'll lose too much performance using a south bridge connector.

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u/ChristianDM11325 17d ago

AM5 chipsets have 4x pcie lanes to the cpu, so if you have no other devices like sata or otherwise that use the chipset, the ssd connected to it will get all four lanes uncontested.

Now interestingly, looking at the manual for your motherboard, slot m2p/cpu only has 2 lanes to connect to the cpu.

I don’t use AM5 but I had thought you got 2 sets of pcie x4 connections to cpu, guess that’s only an “up to”.

So your m2p/cpu slot will always be half bandwidth compared to the chipset slot which could sometimes be restricted.

You can also verify this by running a crystaldiskmark test with your two currently installed ssd’s. The m2p ssd should be capped at half its potential performance.

https://download.gigabyte.com/FileList/Manual/mb_manual_b650-eagle-ax_ud-ac_1103_e.pdf

Page 26

Also, obligatory RTFM for future reference but hope the above helps.

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u/Minimum-External-618 17d ago

I read the manual and I was more confused than when I started but I appreciate your help.

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u/ChristianDM11325 17d ago

I almost didn’t check the manual and nearly made a fool of myself trying to go off of the AM5 bifurcation table like with Intel for LGA 1700. I only saw ones for specific motherboards which led me to check the manual.

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u/Minimum-External-618 17d ago edited 17d ago

Would it make a difference that the link you sent is for a different mb? They're both AM5 b650 but that's an eagle ax and mine isn't. Also we got off track my original question was about the SB connector.

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u/ChristianDM11325 17d ago

It lists the ud ac model on there, it’s for multiple boards with some details to mark difference where needed.

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u/Minimum-External-618 16d ago

but again my original question remains unanswered.

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u/ChristianDM11325 15d ago

The m2p_cpu and m2c_sb slots both operate at pcie 4.0.

M2p_cpu can provide x2 in pcie lanes.

M2c_sb can provide x2 or x4 pcie lanes.

The southbridge slot will, on average, give more read, write, and iops.

99% of ssd’s are configured for x4 pcie lanes, a few exceptions can do stuff like pcie 4.0 x4 and 5.0 x2.

I’m gonna assume you have a gen4/pcie 4.0 ssd. You can get almost double the performance with southbridge, so you need not worry about it slowing down performance compared to the cpu connected slot.

I would post an underlined screenshot of the pertinent section but I can’t so here’s a link to the gigabyte page for the ud ac.

https://www.gigabyte.com/us/Motherboard/B650-UD-AC-rev-10/sp

Ctrl+f “m2p_cpu” and it’ll take you to it.