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Why does Windows only show about 3.5 GB of my more than 4 GB of RAM?

we have DELL Precison 670 machines. we installed 4 1GB memory slips. From the BIOS we can see 4 of them. but in WinXP, the OS says we only have 2.5GB. Why 2.5GB?

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migrated from serverfault.com Mar 21 '11 at 21:10

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marked as duplicate by Sathya Aug 28 '12 at 10:22

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2 Answers 2

up vote 6 down vote accepted

My Guess is you've got a 32bit OS, so your limit is down to 3.5GB then you've probably got the onboard video cranked up to the max utilizing the missing 1GB of RAM. You should be able to turn the video down or just pickup an actual video card and pop it in to regain the other 1gb or RAM.

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we installed an NVidia GeForce video card. Are you saying we can configure the machine to use the installed video card and regain the other 1GB RAM? how to do that? –  5YrsLaterDBA Mar 21 '11 at 19:59
    
+1 one would think that the Mobo would be smart enough to divvy out the unusable ram for the video card... –  JeffG Mar 21 '11 at 20:00
1  
@Jeff - one one think so but I've seen Dell Precision's do some really dumb things with their on-board video. –  Mark Henderson Mar 21 '11 at 20:36
    
@Student - Check the BIOS, theres probably some settings in there for disabling the onboard video or reducing the onboard video memory consumption. –  ErnieTheGeek Mar 21 '11 at 20:46
    
Memory is NOT automatically limited to 3.5 GB just because you use a 32 bit operating system. Hardware devices require address space so that the system can talk to the devices. Before 4 GB was anywhere near common, it was decided to use the UPPER regions of memory (starting at the 4 GB Limit and counting backwards) for that address space. If you have a 1 GB video card, that's a LARGE address space needed counting back from 4 GB - but video cards are NOT the only devices that need address spaces - most if not all hardware does - network cards, sound cards, etc. –  Multiverse IT Mar 21 '11 at 22:43

Windows XP has a 4GB physical memory limit, but things like graphics cards and other devices can affect this. Userland memory is also limited to 2GB.

Take a look at this: http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx

And this: http://www.brianmadden.com/blogs/brianmadden/archive/2004/02/19/the-4gb-windows-memory-limit-what-does-it-really-mean.aspx

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