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Possible Duplicates:
Where did the other .8 GB of RAM go?
Windows x86 physical memory is 24-bit?
Why is usable RAM less than total RAM?

I have a computer with 4GB RAM. Why isn't it all usable? What does this mean?

See below:

Installed: 4GB, Usable: 2.9GB

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marked as duplicate by quack quixote, Molly, Troggy, Diago Nov 25 '09 at 5:38

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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Dude - where's my 4 Gigabytes of RAM > codinghorror.com/blog/archives/000811.html –  Sathya Nov 24 '09 at 21:46
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A better question might be "Why does this dialog in Windows 7 not explain why less than 4GB is usable?" –  JMD Nov 24 '09 at 21:53
    
@JMD: Would be nice if Microsoft would just put the answer in Windows, wouldn't it? –  TheSmurf Nov 25 '09 at 4:09

2 Answers 2

It's because you have 32bit installed. 32 bit can only go so high. You need 64bit.

If you do have 64bit, 1Gb of RAM may be shared with the video card.

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This is purely a limitation of the 32-bit operating system, and has been around since XP. Vista SP1 had an update that changed the dialog to show 4GB, but in reality, the OS was still only using 3.

The reason: Windows 32-bit can only use 4GB of memory. This applies to ALL hardware, including your video card.

If your video card has 1GB of VRAM, this means you're trying to use 5GB total. The BIOS often has settings to choose the amount of memory dedicated to your video card, and Windows will use as much RAM as it can in the remaining space.

Here is an external reference with people stating the same thing.

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Actually it's not Windows deciding that the video card is more important. The hardware memory space is always mapped below the 4 GIB boundary. Also it can also be a chipset limitation. My ThinkPad R60 only allows for 3 GiB of RAM even with a 64-bit OS. –  Joey Nov 24 '09 at 21:44
    
Assuming the chipset allows for 4GB, it usually is a BIOS option to change the amount of memory dedicated to video. Edited that part, since in either case, it really is the chipset deciding this. –  Will Eddins Nov 24 '09 at 21:48

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