Physical Memory Limit
The physical memory limit depends on which version of Windows you have. However the usable memory (which may be less than the installed memory) depends on other factors (see below).
You have Windows 7 Home Premium (64 bit). According to the above table the maximum physical memory is 16 GB.
Source Physical Memory Limits: Windows 7
Usable Memory
All of the physical memory may not be usable.
On a computer that is running Windows 7, the usable memory (RAM) may be less than the installed memory.
The reduction in available system memory depends on the configuration
of the following:
- The devices that are installed in the computer and the memory that is reserved by those devices
- The ability of the motherboard to handle memory
- The System BIOS version and settings
- The version of Windows 7 that is installed (For example, Windows 7 Starter Edition only supports 2 GB of installed memory.)
- Other system settings
If you have a video card that has 256 MB of on-board memory, that
memory must be mapped within the first 4 GB of address space. If 4 GB
of system memory is already installed, part of that address space must
be reserved by the graphics memory mapping. Graphics memory mapping
overwrites a part of the system memory. These conditions reduce the
total amount of system memory that is available to the operating
system.
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Check BIOS settings
The problem may occur because some BIOS settings are incorrect.
Enable the memory remapping feature
Check the BIOS settings to see whether the memory remapping feature is
enabled. Memory remapping gives Windows access to more memory. You can
enable the memory remapping feature in the BIOS by booting to the
system setup. See the User's Guide for your computer for instructions
on how to boot to system setup on your computer. The name for the
memory remapping feature may be different for different hardware
vendors. This can be listed as memory remapping, memory extension, or
something similar. Be aware that your computer may not support the
memory remapping feature.
Change the AGP video aperture size in the BIOS settings
Check the BIOS settings to see how much memory that you have allocated
to AGP video aperture. This is the memory that the system is sharing
with the video card that is used for texture mapping and rendering.
This memory would not be used by the system, because it is locked by
the video card. You can adjust the AGP video aperture size in the
BIOS. Standard settings are "32MB,""64MB,""128MB,"and "Auto." After
you change this setting in the BIOS, restart your computer, and then
check the usable memory. You can test each setting to see which offers
the best results.
Source The usable memory may be less than the installed memory on Windows 7-based computers