4GBs of RAM, but only Showing 3GB

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Lee W, MVPConnect With a Mentor Technology and Business Process AdvisorCommented:
If the computer doesn't support 36 bit addressing, this is probably normal.  Areas of upper memory are reserved for other hardware.
Some more information:
32-bit OSs can only address 4GB RAM. If you have a page-file (by default), then this will take up this address space. For example, with a 1.5GB pagefile, your machine will only show 2.5GB RAM.

You could remove the page file by setting its size to zero, in which case you will see the full 4GB.
make sure that motherboard support up to 4 GB look at data sheet
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Lee W, MVPTechnology and Business Process AdvisorCommented:
rbowall is partly correct.  32 bit OSs can only address 4 GB of RAM.  But windows gives each application 4 GB of RAM address space even though most will never come close to using it.  The pagefile is used to store things that are in RAM but not used much.  One of my servers has 2.25 GB of RAM and a 3.5GB page file.  And the total available RAM (as reported by Task Manager under "Commit Charge (K) in the performance tab is roughly 5.75 GB (5800816).
David Johnson, CD, MVPOwnerCommented:
a 32bit cpu can only address 4G maximum. This includes your bios rom, video memory, io-mapped ports (usb/ide etc)
I am pretty sure that it is actually a limitation of windows XP that it can only actually use 3 gigs of memory. This article helps a bit.


Also, it depends on the OS you are running, and also if you have onboard video, it can be configured to "Borrow" memory and that can affect how much you have available.
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