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I have a nice laptop - 32 GB of RAM, M2 (SATA) and 2.5' SSD (also SATA) - dual boot, Fedora 33 & Windows 2019 Server.

I ran dmidecode and found a Maximum Capacity of 64GB - but the manufacturer (ASUS) says 32GB is the max!

Now, I know that dmidecode isn't perfect, but I want to hear from those who have upgraded their RAM based on dmidecode despite the manufacturer's recommendations?

Quote from link above:

Beware that DMI data have proven to be too unreliable to be blindly trusted. Dmidecode does not scan your hardware, it only reports what the BIOS told it to.

I also found this, which doesn't inspire confidence, where it says:

Aniruddh yes the H300's only support 32gb ram max (officially) its not the cpu support in this case its the mobo limited/locked support all bios are locked so unless its a modded bios (which i strongly dont recommend doing neither its allowed to discuss anything about it in this community ) probably it wont support so until someone buys 32gb sodimms and test them theres no way to know if its will support or not and i doubt anyone would take such a risk on a such high priced ram without having sure if it would really work or not but anyway of you are willing to go for it also why would u need 64gb 32 its already too much no one will ever use them in full and its not having 64gb that would make the laptop faster in some rare cases too much unused ram could also cause some bottleneck and decrease the performance but good luck :)

So, it appears even if the mobo specs allow a certain amount of RAM, the manufacturer may or may not have reduced this capacity from within the BIOS?

Have I grasped the picture - am I taking a big chance going by dmidecode or should I persevere?

Any references/URLs, tips - anything appreciated!

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Ecample: 4 socket supermicro server with 512GB of installed RAM, which is done via 32 x 16gb DIMMS.

dmidecode | grep "Maximum Capacity"

    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB
    Maximum Capacity: 384 GB

also reported from dmidecode for me:
    Locator: P1-DIMMA1
    Bank Locator: NODE 1
    Locator: P1-DIMMA2
    Bank Locator: NODE 1
    Locator: P1-DIMMA3
    Bank Locator: NODE 1
    Locator: P1-DIMMB1
    Bank Locator: NODE 1
    Locator: P1-DIMMB2
    Bank Locator: NODE 1
    Locator: P1-DIMMB3
    Bank Locator: NODE 1
    Locator: P1-DIMMC1
    Bank Locator: NODE 2
    Locator: P1-DIMMC2
    Bank Locator: NODE 2
    Locator: P1-DIMMC3
    Bank Locator: NODE 2
    Locator: P1-DIMMD1
    Bank Locator: NODE 2
    Locator: P1-DIMMD2
    Bank Locator: NODE 2
    Locator: P1-DIMMD3
    Bank Locator: NODE 2
    Locator: P2-DIMMA1
    Bank Locator: NODE 3
    Locator: P2-DIMMA2
    Bank Locator: NODE 3
    Locator: P2-DIMMA3
    Bank Locator: NODE 3
    Locator: P2-DIMMB1
    Bank Locator: NODE 3
    Locator: P2-DIMMB2
    Bank Locator: NODE 3
    Locator: P2-DIMMB3
    Bank Locator: NODE 3
    Locator: P2-DIMMC1
    Bank Locator: NODE 4
    Locator: P2-DIMMC2
    Bank Locator: NODE 4
    Locator: P2-DIMMC3
    Bank Locator: NODE 4
    Locator: P2-DIMMD1
    Bank Locator: NODE 4
    Locator: P2-DIMMD2
    Bank Locator: NODE 4
    Locator: P2-DIMMD3
    Bank Locator: NODE 4
    Locator: P3-DIMMA1
    Bank Locator: NODE 5
    Locator: P3-DIMMA2
    Bank Locator: NODE 5
    Locator: P3-DIMMA3
    Bank Locator: NODE 5
    Locator: P3-DIMMB1
    Bank Locator: NODE 5
    Locator: P3-DIMMB2
    Bank Locator: NODE 5
    Locator: P3-DIMMB3
    Bank Locator: NODE 5
    Locator: P3-DIMMC1
    Bank Locator: NODE 6
    Locator: P3-DIMMC2
    Bank Locator: NODE 6
    Locator: P3-DIMMC3
    Bank Locator: NODE 6
    Locator: P3-DIMMD1
    Bank Locator: NODE 6
    Locator: P3-DIMMD2
    Bank Locator: NODE 6
    Locator: P3-DIMMD3
    Bank Locator: NODE 6
    Locator: P4-DIMMA1
    Bank Locator: NODE 7
    Locator: P4-DIMMA2
    Bank Locator: NODE 7
    Locator: P4-DIMMA3
    Bank Locator: NODE 7
    Locator: P4-DIMMB1
    Bank Locator: NODE 7
    Locator: P4-DIMMB2
    Bank Locator: NODE 7
    Locator: P4-DIMMB3
    Bank Locator: NODE 7
    Locator: P4-DIMMC1
    Bank Locator: NODE 8
    Locator: P4-DIMMC2
    Bank Locator: NODE 8
    Locator: P4-DIMMC3
    Bank Locator: NODE 8
    Locator: P4-DIMMD1
    Bank Locator: NODE 8
    Locator: P4-DIMMD2
    Bank Locator: NODE 8
    Locator: P4-DIMMD3
    Bank Locator: NODE 8

i believe my server is quad channel ram and with 4 cpus the reason for all of everything shown above. However note the "max capacity" of 384gb reported, how/where that it listed {which I did not indicate above} each is for a Physical Memory Array. It gets complicated and you have to dive into the memory channel specifics to get an accurate understanding... but my server does not have a max capacity of 384gb ram nor does it have a max capacity of 3072 gb. I believe based the true max ram available to the operating system is based on cpu/memory architecture; for me is 768gb and I think under certain circumstances (for other servers) can be 1.5tb if using certain low voltage DIMMS and the [server] BIOS supports it. Note however the that does not correspond to the reported number of 384, which are all listed under Physical Memory Array in my case. So it is a matter of interpretation, or misinterpretation rather. This Maximum Capacity does not refer to the maximum amount of usable RAM seen by the operating system, it is reporting a low level memory channel interface. So while i don't doubt dmidecode is not 100% reliable regarding every bit of hardware it is interfacing, you have to really dive in and understanding what values it is trying to report on.

Your laptop being 1 cpu and I suppose 2 memory channels vs a 4 socket server like I listed above... obvious differences aside based on what you said for your specific laptop I suspect you are seeing a max capacity of 64gb at the hardware manufacturer memory channel level but in the end that Asus laptop it will be that Asus bios code being what's really in charge. If Asus says only supports 32gb I would believe that because it's that bios code making that happen not the hardware memory channel capability of 64gb being reported by dmidecode. It would be getting down to computer engineering level- i suspect ASUS (and everyone else) use all the same memory channel type hardware which is capable of referencing a 64gb DIMM but there's other hardware in play which makes a 32gb limit actually happen. I wouldn't necessarily go thinking ASUS simply programmed BIOS code to simply limit the laptop to 32gb when it really could have 64gb.

You also mentioned H300, which is an intel chipset... recognize any consumer pc motherboard like that has only 2 DIMM slots vs 4 DIMM slots of a higher end Z370 chipset for example... all those 2 DIMM motherboards are all limited to 32gb total RAM vs 64gb total ram of the 4 DIMM motherboards. So I would not try to put 64gb of ram in your laptop it's not going to work. I can also tell you fwiw I've tried installing Windows 7 pro on my 512gb server and only 192gb shows up as usable in Windows.

why would u need 64gb 32 its already too much no one will ever use them in full and its not having 64gb that would make the laptop faster in some rare cases too much unused ram could also cause some bottleneck and decrease the performance but good luck :)

unused ram does not cause bottleneck or decrease performance. That answer is out of context and neglects a lot of low level architecture and memory channel layout which is the reason why/how ram quantities can affect performance [at the hardware level]. And luck has nothing to do with it.

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The real question is not dmidecode itself being trustworthy but whether the information it reads is actually reliable or not. As quoted in your question, dmidecode does not effectively scan your hardware, but instead reads some data stored in the BIOS for any kind of management software (Desktop Management Interface, DMI spec. on the DMTF site).

This data is a list of formatted strings made by the BIOS manufacturer.

dmidecode is reliable, but these strings (as any software component) are subject to bugs / too quick copy-paste / not being up-to-date. I guess this is what you're experiencing now.

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