Re: Memory question

From: Edward Sanford Sutton, III <>
Date: Tue, 03 Jan 2023 13:27:15 UTC
On 1/3/23 06:04, Eivind Nicolay Evensen wrote:
> Hello.
> This might be more related to a bios setting or issue, but I hope
> somebody can give me hints in the right direction to remedy or
> at least diagnose this issue further.
> I installed more memory in one machine and now I see this
> in dmesg:
> real memory  = 25769803776 (24576 MB)
> avail memory = 8237150208 (7855 MB)
> Real should be right, from before there were two 4 GB dimms in there,
> and I inserted two more 8 GB ones.
> Transcribed from BIOS:
> DIMM(s)			1		2		3		4
> Installed Size		8192		8192		4096		4096
> Enabled Size		8192		8192		4096		4096
> Total Size		24576
> I was wondering if the reason could be that this machine has been updated
> since older versions and bootloader may be old or whatever, so I also tried
> booting a linux. However, that also only uses 8 GB, and says (at least in a
> way I understand) less about what it can really see.
> This is amd64 FreeBSD 13.1.
> Is there any way I can use the rest of the memory? Or at least find out
> which dimms it is actually using?

   I agree. A BIOS update may also impact on what memory is supported 
too. It is usually for the better bot not always.
   Some memory uses fewer but more dense chips while others use more but 
less dense memory chips and which is supported can vary. Sometimes a 
memory manufacturer revises a stick and it may alter its compatibility 
too. You can also attempt to remove 1 to 3 sticks to see how it is 
handling the 8GB modules. They may have incompatible specifications 
where the system may stop booting if you do not have a 4GB stick in or 
even depending which slot it is in. If something is only a little out of 
tolerance then you may be able to try different sticks in different 
slots to bring them online.
   I usually recommend checking memory manufacturers for what they will 
claim they tested their memory modules with instead of the motherboard 
manufacturer as motherboard manufacturers do not test all sticks out 
there (=unnecessarily small compatibility list) and do not usually 
update their compatibility chart as BIOS updates and different CPU's 
built in memory controllers impact it.
   If you lookup specs for your related memory controller, you may find 
it has a limited amount of RAM supported. It is doubtful, though not 
impossible, that a BIOS update will bypass such a limitation. For Intel 
processors I usually just do a google search for ark + processor model 
to see max supported memory. ark pages are where you find 
processor specifications in an easy layout for their chips. Wish I knew 
of comparable lookups for AMD, ARM, etc.