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I have an old mini-PC (Acer R3610 Revo) that I've repurposed as a general server (docker containers mostly). It has 4GB of physical RAM installed (specs and BIOS show it) but only ~3GB is accessible to Ubuntu. It's running Ubuntu 18.04.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:    18.04
Codename:   bionic

After some reading it looked like it could be due to PAE (or lack there of) but it's running the 64-bit version and to my knowledge that should mean PAE is installed by default.

$ uname -a
Linux master_control 4.15.0-193-generic #204-Ubuntu SMP Fri Aug 26 19:20:21 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

However when I check the kernel there's no mention of PAE like a lot of the online resources say there should be.

$ uname -r
4.15.0-193-generic

Out of curiosity I attempted to install the pad kernel anyway but it was unable to find the package.

$ sudo apt-get install linux-generic-pae linux-headers-generic-pae
[sudo] password for master: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package linux-generic-pae
E: Unable to locate package linux-headers-generic-pae

I did some quick googling and gave up pretty early since I was unsure if that's even the correct route to take under the circumstances.

I thought maybe some of the memory is hardware reserved and went into the BIOS and switched the video memory setting from Auto (was 256MB) to 64MB (the lowest I can go and still get display output). This helped a little taking it from about 2.93GB available in Ubuntu to 3.11GB (according to htop and other output).

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           3.1G        1.3G        368M        3.4M        1.4G        1.7G
Swap:          2.9G          0B        2.9G

There is this discussion that is quite similar but 1GB seems excessive to be used by... I'm not sure what if the APU has been limited to just 64MB 64bit system sees only 3GB of 4GB RAM

Curious if I'm able to free up the last ~1GB or so for Ubuntu or if it's likely hardware reserved or otherwise just not accessible at all.

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  • Are you using a 32-bit version of Ubuntu? If not, then I'd suggest hardware problems are at fault. If you are, is your system 64bit compatible? If so then have you considered running a 64bit install?
    – Thomas Ward
    Sep 28, 2022 at 23:31
  • Looking at this page ubuntuforums.org/archive/index.php/t-1245699.html it seems that the consensus back then was that this is an Acer problem. No one there could fix it and it was only showing 3GB in both Windows and Ubuntu.
    – Terrance
    Sep 28, 2022 at 23:53
  • You might also want to see: forum.kodi.tv/showthread.php?tid=94384
    – Terrance
    Sep 28, 2022 at 23:57
  • Even after reading this one sysnative.com/forums/threads/… I very highly doubt you are going to see all 4GB available to the OS.
    – Terrance
    Sep 29, 2022 at 0:02
  • @ThomasWard I specifically mention in the OP that I'm using the 64-bit version, as far as I can tell. It's not likely a hardware problem. The BIOS shows all 4 GB and the output of a Linux command (forget which one) shows two 2GB sticks. I can't imagine what kind of hardware problem would only allow an OS to utilize part offs stick of RAM, it's clearly able to interact with both if it's even showing over 2GB. Sep 29, 2022 at 2:02

1 Answer 1

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Thanks to @Terrance for some additional posts I did not find in my searching. Looks like it's by design with Atom based machines (or at least these Acers). Seems like a common issue nobody has overcome with these and this post suggests about the amount I'm missing is reserved for other hardware.

Aspire Revo R3600 or R3610 recognizes 3GB of RAM / Why does my Aspire Revo R3600 or R3610 only recognize 3GB of RAM memory out of 4GB?

If you have 4GB of Random Access Memory (RAM) installed in your Aspire Revo R3600 or R3610, the operating system recognizes it as only 3GB. This is not due to any software limitations, but to the architecture of the Atom processor.

CAUSE

Due to its design, the Atom processor can address up to 4 GB of RAM. Parts of the memory will be assigned to hardware resources during the start-up of the system, making this memory invisible for the Operating System.

RESOLUTION

This is expected product behaviour due to its design, and it does not indicate a product failure or bug.

MORE INFORMATION

The System missing memory is used in the following way:

  • 256 megabytes (MB) is assigned as video memory.
  • A total of 512 MB is used for PCI hardware resources.
  • 256 MB is dedicated to PCI Express hardware resources.

Would make sense being that after I reduced my video memory to 64MB I got a bit back in the OS and the remaining 768 MB or so used by the PCI resources would bring be close to 4GB minus some rounding.

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