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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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Dude - where's my 4 Gigabytes of RAM > codinghorror.com/blog/archives/000811.html – Sathya Nov 24 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 at 21:53
@JMD: Would be nice if Microsoft would just put the answer in Windows, wouldn't it? – DannySmurf Nov 25 at 4:09

closed as exact duplicate by ~quack, Molly, Troggy♦, Diago♦ Nov 25 at 5:38
This question covers exactly the same ground as earlier questions on this topic; its answers may be merged with another identical question.

3 Answers

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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. – Johannes Rössel Nov 24 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 at 21:48
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http://www.letmegooglethatforyou.com/?q=windows+7+not+using+4GB+RAM

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-1 Not an answer. – Troggy♦ Nov 24 at 22:49
No, but since I can't vote to close this question that people have peppered this site, and every Windows forum on the Internet with..... – DannySmurf Nov 24 at 22:51
@DennySmurf: This is a comment at best, not a solution. You can vote to close questions with 3k+ reputation. If you do not have the required reputation, then flagging the question for moderator attention is the proper course of action. Then just leave a note about whatever is the issue with the question. (duplicate, offensive, etc.) – Troggy♦ Nov 24 at 23:00
No, it's not a solution. It's an answer, given snarkily, because the original poster neglected to do five seconds of research before asking. Not interested in the "appropriate course of action;" this is Q&A, not a Senate debate, so relax a bit. These sites are supposed to be fun, remember? Be a rules stickler to someone else, thanks. – DannySmurf Nov 25 at 4:31
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@DannySmurf. Google it is not valid answers for SU. Period. Google is the SU home page. This is your one and only warning. – Diago♦ Nov 25 at 5:39
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