Question 4GB of DDR2 RAM read only as 2.5GB - how to fix?

Oct 14, 2021
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So I have this old office PC that had a single stick of 1GB DDR2 RAM, and I decided to upgrade to 2 sticks of 2GB RAM. But for some reason, the BIOS only reads 2.5GB of this.

What I've done so far:
  • Installed Windows 10, 64-bit version, to remove any chance of OS limitations. Still 2.5GB.
  • Checked the BIOS for any sort of memory-limiting option. Found none.
  • Checked both sticks individually. Both read as 2GB. None of them are duds.
  • Put one of the 2GB sticks with the old 1GB stick (3GB total), to see if I don't have some arbitary 2.5GB RAM cap. Nope! 3GB total, both on BIOS and Win 10.
  • Tried to find the motherboard online for specs. Closest match is the MSI P4M900M2-L (https://www.msi.com/Motherboard/P4M900M2L/Specification), which claims to only read 2GB total. See previous line on why that's a lie.
At this point, I've run out of ideas. What can I do? Should I update the BIOS?
 

Zerk2012

Titan
Ambassador
So I have this old office PC that had a single stick of 1GB DDR2 RAM, and I decided to upgrade to 2 sticks of 2GB RAM. But for some reason, the BIOS only reads 2.5GB of this.

What I've done so far:
  • Installed Windows 10, 64-bit version, to remove any chance of OS limitations. Still 2.5GB.
  • Checked the BIOS for any sort of memory-limiting option. Found none.
  • Checked both sticks individually. Both read as 2GB. None of them are duds.
  • Put one of the 2GB sticks with the old 1GB stick (3GB total), to see if I don't have some arbitary 2.5GB RAM cap. Nope! 3GB total, both on BIOS and Win 10.
  • Tried to find the motherboard online for specs. Closest match is the MSI P4M900M2-L (https://www.msi.com/Motherboard/P4M900M2L/Specification), which claims to only read 2GB total. See previous line on why that's a lie.
At this point, I've run out of ideas. What can I do? Should I update the BIOS?
run this it should show your motherboard.

You can also run the crucial memory finder
https://www.crucial.com/store/systemscanner

close match is not really good enough.
 
Oct 14, 2021
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Good news! CrucialScan confirms it's an MSI P4M900M2-L!

Bad news: both the MSI spec sheet and CrucialScan confirm that there's a 2GB RAM cap.

This leaves 3 questions:
  1. Why/ How is my motherboard reading 2.5 gigs (or even 3 with that combo mentioned above)?
  2. Why can't it read the rest of the 1.5GBs installed and is there a way to fix it?
  3. Would updating the BIOS help?
 

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