I upgraded to 32 GB of memory on my 2nd computer, and ran into an issue where the BIOS said it was all there, BUT that only 16 GB was available for use.
 
Windows too said 32 GB was installed, but that a little less than half was available.  Looking at detail in the Windows Resource Monitor, it showed that approximately 17 GB was flagged as Hardware Reserved, and this was the missing memory.
 
I looked at a bunch of different potential solutions, including contacting the motherboard technical support, but got nowhere, until I ran across one guy's suggestion that ended up fixing the issue for me.
 
To make a long story short, I went into REGEDIT, then into:
 
HKEY_LOCAL_MACHINE>SYSTEM>CurrentControlSet>Control>Session Manager>Memory Management
 
Once there, I reviewed the ClearPageFileAtShutdown parameter's value, which was set to the Windows default value of binary zero.  That default tells Windows to leave the PageFile contents as they are, when the computer is shutting down.  FYI - sensitive data can remain in the PageFile contents and can be read by someone with access to the computer.
 
I altered the value of ClearPageFileAtShutdown to binary '1' and then backed out and shut down the computer, rather than just doing a restart.  Apparently, just doing a restart, even with that parameter set to '1', doesn't clear out that file - has to be a shut down.
 
Anyways, upon restart, sure enough, the missing memory was once again available to Windows, so that I had the entire 32 GB of memory (minus normal Windows overhead).
 
IF anyone else runs into issues where about half your memory is showing up as unavailable, and flagged in Resource Monitor as Hardware Reserved, you might think about backing up the Registry and looking into performing the above.
 
I certainly cannot guarantee it will work, but it certainly took care of it for me.....
 
Bob Bone
 

That's good information, Bob!  One caveat should be noted: As you said, setting this flag to one, in addition to clearing up your memory problem, causes the OS to overwrite the entire pagefile every time the machine is shutdown. This is fine unless your pagefile is on an SSD volume, in which case that kind of hammering could impact the life of the drive. If you're going to go this route, you should probably move the pagefile itself to a standard hard drive.
 
One other thing I saw cause this particular problem (in fact, the only time I saw this problem myself) was a BIOS that needed updating on one of my laptops. After the BIOS update, all the new memory was available.
 
Here's a link to a Microsoft knowledgebase article on that issue that I used.
 
https://support.microsoft.com/en-us/kb/978610

Sounds reasonable - I have the latest BIOS.  So far so good with the change I noted above.
 
Bob Bone
 

robert_e_bone
Sounds reasonable - I have the latest BIOS.  So far so good with the change I noted above.
 
Bob Bone
 

Is it possible to reset value to zero later - once booted and creating fresh pagefile with extra memory?
Thinking if it was something at first boot and existing pagefile was from before memory was increased.
And you won't need to recreate pagefile every boot either.

UPDATE: I did more digging, and discovered that while the registry change I noted above to clear out the pagefile on shutdown is still something I wish to do, it did NOT always guarantee proper allocation of hardware reserved memory in Windows.
 
So, I ended up making the following change, and this time it seems to repeatedly leave me with all but a couple GB of memory available to applications on start up:
 
1. Launch MSCONFIG
2. Click on Boot tab
3. Click on Advanced
4. Remove the check labelled: Maximum Memory
5. Click OK and if needed then click Apply and exit MSCONFIG
6. Restart computer
7. Launch RESMON (Windows Resource Monitor)
8. Make sure Hardware Reserved value reported is something sane, like 1-2 GB at most.  (I have 32 GB memory)
9. Win a Grammy for your songs written with your super powerful and super fast Sonar. (consider punching Kanye if he interferes with your acceptance speech).
 
EDITED to add link to Microsoft article describing all but the Kanye/Grammy parts:
 
https://support.microsoft.com/en-us/kb/978610
 
Bob Bone
 

yes, after the grammy's, folks who had never heard of kanye, suddenly knew who he was.
marketing genius

Hey Bob ,
 
I'm still in the single digits stage of RAM on my Win computers .
Some day I hope to make it into the double digits stage when it comes to installed Ram .
 
Thank you for sharing this type of thing ,
 
Kenny