Difference between Installed and Total memory in Windows 2008 server

We've just added memory to our windows 2008 64 bit server.
It originally had 12Gb, and we added another 16gb to make 28gb.

Windows recognize the added memory but it says:
INSTALLED MEMORY 28GB (12 GB Usable)

And in Resource Monitor it says:

Hardware reserved = 16396MB
In Use = 12154 MB
Modified = 3MB
Standby = 117MB
Free = 1MB

Available = 118MB
Cached = 119MB
Total = 12276MB
Installed = 28672 MB

My questions are:
1. Can someone please explain what this means?
2. Is the additional 16 gb being used? I know windows recognized it (hence the "Installed" is 28GB) but why is the "Total" is only 12GB?
3. We run virtual computers on this server. Assuming 1 virtual comp is using 1GB, we hope to run another 16 virtual comp. But before we do that, I wanted to confirm that all memory are recognized and used?

Thank you
SW111Asked:
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SW111Author Commented:
I think I have a standard version of windows 2008 R2 64 bit.
DOnt know how to check it, but I seem to recall buying the standard version.
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Lee W, MVPTechnology and Business Process AdvisorCommented:
What kind of server?  Check the BIOS config - is memory set to mirror?

Do you have multiple CPUs or just one.  Sometimes the hardware may not allow the OS to fully recognize the RAM depending on configuration and CPU (I have a client with a Dell T605 server that only has one CPU and so only supports 16 GB but adding a second CPU can allow it to support 32 GB.
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SW111Author Commented:
Thanks for the link teomcam.
But I'm not really sure I understand why the difference between "Total" and "Installed" is so big...
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SW111Author Commented:
Leew, its an IBM server with 2 cpu.
But I think the oS recognize the RAM, only that it's not making it available to use.
Because "Total" is 12276 MB and "Installed" is 28672MB

The physical ram size is shown correctly on the "Installed" information.
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Venugopal NCommented:
The below link will provide the RAM supported by the OS.

http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx

Did you check if the hardware support the 32GB RAM?
Did you migrate the OS recently?
Did you tried with the RAM remapping in BIOS & in Bois what is the RAM capacity it show?
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andyalderSaggar maker's bottom knockerCommented:
To get the total memory value Windows asks the baseboard management controller and the BMC asks the DIMMs via the SPD bus. So where you say Windows recognizes that doesn't mean through the address/data lines but via management signaling on the mobo. Any difference between what Windows can actually see through the address/data lines and what is reported by the BMC is reported as hardware reserved.

There are various reasons for Windows not being able to address the RAM, it can be installed on the wrong CPU on single CPU systems, you can fit UDIMMs plus RDIMMs in which case the mobo won't enable the sockets, you may have mirrored memory as leew mentioned or you may just have faulty RAM that the mobo detected and disabled.

Part numbers of the original RAM and the new RAM will help, CPU-Z will get that info for you, there's both a memory and SPD tab on it. http://www.cpuid.com/softwares/cpu-z.html
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SW111Author Commented:
Andyalder,
So far that I know, the memory was recommended by IBM distributor because they had asked for the serial number of our server.
But in any case, what do you propose me to do? Install the cpu-z software and post the parts number?
I will try to do this on monday. Thanks
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andyalderSaggar maker's bottom knockerCommented:
They probably looked it up on IBM's web to see what it was supplied originally with, but that's not infallible. I can check when you post the part numbers, there may be an IBM equivalent online diagnostic to list the FRUs rather than CPU-z but that should work OK anyway.
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SW111Author Commented:
Andalyder,
I've looked up the information you requested.
If I don't really have to, I prefer not to install softwares on the server. So here is the infor based on visual and purchase confirmations:

1. The server:
System X 3620 M3 / 737622A
Serial: 737622A-062P812
There's another number I'm not sure of: PNSN 94Y6028 YK10LN16R0BN
Workorder number: 38CF36PM

2. The newly added memory brand is IBM: 49Y1397, 8GB, PC3L-10600 EXX RDim
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SW111Author Commented:
turns out the computer shop made an error in installation and didnt follow the slotting sequence properly.

thanks
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SW111Author Commented:
fixed it and hardware reserved is now only 12 MB. I guess thats fine?
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