dnyvdm
Bronze

Dell XPS 15 9550 32gb only 25.4gb usable

My Dell XPS 15 9550 has 32GB RAM but Windows 10 (build 1703) reports that only 25.4 GB is usable from the 32GB.

In the bios I cannot find any settings that have any influence on this.

Anyone seen this before? I would like the have the full 32GB available (for running VM's in Hyper-V)

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17 Replies
ejn63
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

There is no way to free up all system memory - the operating system requires a certain amount to function.

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jphughan
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

@ejn63, that "usable" metric doesn't subtract the amount of memory the OS consumes.  I've checked 2 systems, one running Win10 1607 and the other running Win10 1709 (both with Hyper-V installed, incidentally) and I don't see that "usable" metric at all.

That's typically seen on 32-bit systems because some devices (like integrated GPUs) use system memory as video memory, and some other hardware devices even when they have their own memory need to reserve a block of address space from the system-wide pool to refer to their own memory -- which means that actual system memory can't use that address space even though capacity is technically available.  But on a 64-bit system, the address space pool is so large that this isn't an issue anymore.  Do you have any "unusual" peripherals connected to your system at the moment, such as an external GPU via Thunderbolt?  If so, do you still see this metric if you boot your system with no external peripherals attached?  Also, do you have a Samsung retail SSD with "Rapid Mode" enabled, which uses a block of system memory essentially as a huge cache?

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dnyvdm
Bronze

RE: Dell XPS 15 9550 32gb only 25.4gb usable

I have no unusual peripherals connected but I did switch the factory default SSD for a Samsung 960 EVO 1TB SSD M.2 but Samsung's Magician tool says that Rapid mode is not supported for this SSD.

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dnyvdm
Bronze

RE: Dell XPS 15 9550 32gb only 25.4gb usable

Windows Resource monitor does show 6,7GB reserved for hardware

So if this is not the SSD then the Geforce GTX 960M is only thing left that could claim such an amount of memory for hardware. 

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jphughan
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

Rapid Mode isn't supported for NVMe SSDs, so that's expected, but in that case it wouldn't account for a large chunk of memory missing.  I don't have any immediate suggestions left in that case, but I'll do a bit of research as I have spare time because I'm rather curious about this now.  And if you find the answer yourself, please report back.

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jphughan
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

Just saw your new post with Resource Monitor.  I agree the GeForce GPU seems like the only possible culprit that could take that amount of memory, and I admit I don't have experience with other XPS systems that have 32GB of memory installed; my own XPS 15 only has 16 and I don't have this issue.  It's certainly possible that my understanding is incomplete on this, but from what I do know, I'm not sure why the GPU would cause this behavior.  First, the GPU definitely has physical memory dedicated to it; the GPU does not reserve actual system memory to use as video memory.  And second, even if it required a block of address space, that shouldn't cause a large hardware reservation like that.  Even if it needed to reserve address space below the 4GB barrier, which many GPUs do, the rest of the system's memory should still have no problem mapping to a higher address space, since the 64-bit architecture offers enough address space for some outrageous amount of memory.  And in that case, you wouldn't lose that amount of usable memory.

Like I said, I'll keep digging on this because I'm curious myself.

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jphughan
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

Quick question: Did the system ship with 32GB of RAM, or did you add more yourself?  Apparently one possible cause of memory being "Hardware Reserved" is when the system detects that at least part of it is bad.

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dnyvdm
Bronze

RE: Dell XPS 15 9550 32gb only 25.4gb usable

It shipped with 16GB and this was replaced by 32GB Crucial DIMM's

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jphughan
Diamond

RE: Dell XPS 15 9550 32gb only 25.4gb usable

Ok, so you completely removed the original memory and installed a matched pair of 2x16GB instead.  In that case, one way you can identify a bad module would be to remove one of them.  Boot the system and see if it shows 16GB of memory with all of it usable.  If so, replace that single module with the other one and see what happens.  You may find that one of them shows 16GB with only 9.4GB usable or something.

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