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I have 589 Gb of physical memory but Ubuntu will only map 64Gb. e.g.

free -h -t
               total        used        free      shared  buff/cache   available
Mem:            62Gi       1.0Gi        60Gi        39Mi       1.1Gi        60Gi
Swap:          2.0Gi          0B       2.0Gi
Total:          64Gi       1.0Gi        62Gi

But there really is a whole lot more physical memory there. The BIOS detects it. Also:

$ sudo dmidecode | grep -A8 'DMI type 17' | grep Size
        Size: 16 GB
        Size: 16 GB
        Size: 258496 MB
        Size: 16 GB
        Size: 16 GB
        Size: 258496 MB
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed

Can anyone help me let Ubuntu map all that extra memory? I have tried resetting the CMOS/NVRAM, re-seating the memory sticks, re-installing Ubuntu 22.10, tried looking for a BIOS option to release the memory but to no avail. Any help will be very much appreciated. I note that a similar question was resolved by replacing faulty RAM. I will look into that but could there be any other reason? Is it really an Ubuntu issue? I have a Dell Precision 7820 Tower.

[EDIT] I also upgraded the BIOS to the latest version. No effect.

Simone
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    Welcome to AskUbuntu! Are you certain the 256GB sticks you added are compatible with the other RAM sticks? Have you checked whether the motherboard expects the memory to be installed in a Larger⇢Smaller manner? Many times the motherboard will report memory but will not allow an OS to read it if the sticks are mispositioned. – matigo Feb 07 '23 at 02:24
  • The memory was factory-installed. I guess it's possible that they screwed up. For this box, the standard ram sets are only for equal sizes up to 32 Gb per stick. So a total of 384 Gb. I don't know what the order should be for sticks of unequal size. Maybe my memory config is not possible. – Simone Feb 07 '23 at 04:31
  • My inxi output: Memory: RAM: total: 62.45 GiB used: 1.68 GiB (2.7%) Array-1: capacity: 1.25 TiB slots: 3 EC: Single-bit ECC max-module-size: 426.67 GiB note: est. @Terrance it looks like it should handle the bigger ram sticks? – Simone Feb 07 '23 at 23:27
  • Sorry, I didn't even see your reply until now. I was going through looking for some old stuff of mine. Anyways, it looks like inxi might be messing up on that board and not pulling the information correctly. I looked around, and without knowing your CPU type or the types of DIMMs I can only guess. The only info I can find is https://www.dell.com/support/manuals/en-us/precision-7820-workstation/precision_7820_om_pub/memory-specifications?guid=guid-644d2756-8b52-4142-a7dc-dc898ae38dcc&lang=en-us where like ECC type DIMMs only work with the XEON CPU and Non-ECC with X type CPU. – Terrance Jan 09 '24 at 03:00

2 Answers2

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If you run sudo inxi -mx it will show you what the memory array capacity is and what the max module size is (which looks like is brand new to inxi).

So if you divide that by the number of slots in the system that will tell you the maximum capacity of each DIMM you can put in the system. Mine tells me the capacity is 32GB with 4 slots which means that 8GB is the maximum size I can put in each slot.

If your capacity is 384 GB with 12 slots, that means that 32GB is the maximum you can put in each slot.

Example of inxi on my system here:

terrance@terrance-ubuntu:~$ sudo inxi -mx
[sudo] password for terrance: 
Memory:
  RAM: total: 15.61 GiB used: 4.58 GiB (29.3%)
  Array-1: capacity: 32 GiB note: est. slots: 4 EC: None
    max-module-size: 8 GiB note: est.
  Device-1: A0 size: No Module Installed
  Device-2: A1 size: No Module Installed
  Device-3: A2 size: 8 GiB speed: 1600 MT/s type: Unknown
  Device-4: A3 size: 8 GiB speed: 1600 MT/s type: Unknown
Terrance
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It turns out that my large memory sticks are actually Optane PMem sticks, set to Application Direct mode. Reconfiguring them to Memory mode solved the problem.

               total        used        free      shared  buff/cache   available
Mem:           495Gi       760Mi       494Gi       2.0Mi       460Mi       491Gi
Swap:          8.0Gi          0B       8.0Gi
Total:         503Gi       760Mi       502Gi

The relevant page that shows how to configure Optane PMem is: Here

Thanks for all your help and it of course wasn't an Ubuntu issue at all!

Simone
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