4GB ram becomes 2.75GB?

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josh
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4GB ram becomes 2.75GB?

Post by josh »

My motherboard supports 4GB and it used to work, but now as I plug in each stick, as soon as I plug in the third I start loosing huge amounts of "efficiency" or something. If I plug in any one of the four 1GB sticks, it shows 1GB in BIOS (tested) and in windows.

If I plug in any 2, it shows 2GB. As soon as I plug in any 3rd stick, it shows as 2.75GB in BIOS, and the 4th brings it to 3.5GB in bios (only 2.75GB in windows). What should I replace, software? hardware? If the latter, RAM, motherboard? I have not run memtest 86.
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Weirdan
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Re: 4GB ram becomes 2.75GB?

Post by Weirdan »

You're using 64-bit OS, do you?

Also read this: http://en.wikipedia.org/wiki/PCI_hole
josh
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Re: 4GB ram becomes 2.75GB?

Post by josh »

Upgrading to Win 7 x64fixed it. The thing is it has always shown as 4GB in BIOS, all hardware is 64 bit. Could uninstalling a 32bit OS in favor of a 64bit have made the difference?
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Weirdan
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Re: 4GB ram becomes 2.75GB?

Post by Weirdan »

josh wrote:Could uninstalling a 32bit OS in favor of a 64bit have made the difference?
I'd say yes, because 32bit OS is limited to 4GB address space and that includes a lot of address space for interacting with the devices. On top of that windows uses some 500MB of the upper address space for userland <-> kernel communication.
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Benjamin
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Re: 4GB ram becomes 2.75GB?

Post by Benjamin »

Here's a page I found that I think may clarify this issue:

http://www.codinghorror.com/blog/2007/0 ... f-ram.html

In a nutshell, yes you will experience this on 32bit systems, however it's perfectly possible to use 4gb+ on 32bit installs of Linux by installing the PAE extensions.

http://en.wikipedia.org/wiki/Physical_Address_Extension
josh
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Re: 4GB ram becomes 2.75GB?

Post by josh »

All these links explain it showing up as < 4GB in Windows.

What about in the BIOS?
alex.barylski
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Re: 4GB ram becomes 2.75GB?

Post by alex.barylski »

What about in the BIOS?
Thats what has me confused. Perhaps the BIOS is 32bit or just isn't configured to see 4GB?

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Alex
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Weirdan
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Re: 4GB ram becomes 2.75GB?

Post by Weirdan »

josh wrote:All these links explain it showing up as < 4GB in Windows.

What about in the BIOS?
Did upgrading to Win x64 changed what is displayed in the BIOS? If so, BIOS could be monitoring if you're using 64bit os and trying to be helpful displaying what could be used by your OS. Or OS could be flipping some flag there causing BIOS to understand you'd be able to use the whole RAM.
jagannathg
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Re: 4GB ram becomes 2.75GB?

Post by jagannathg »

Hello Josh,

1. A 32-bit OS can support 4GB!! The reality is that not all of that RAM is made available to the OS all the time as the system reserves portions.

2. Dont avoid BIOS updates. They almost always do more good than harm. In the rare times they actually brake existing functionality then yes roll back.

Now to actually answer the question...

There are several factors that come into play regarding the maximum amount of RAM in your computer. The first and most obvious as everyone points out is the architecture of the system (32 or 64 bit) since 32 Bit systems impose a theoretical maximum of 4GB. This number is determined as the maximum number of addressable values a 32 bit number can have.

As some others have pointed out, you dont see all of this memory in windows sometimes but that does not mean it is going to waste! You dont "lose" the RAM its simply being used by the system. (For things like PCI/PCI-X, graphics e.t.c.)

Finally there are some other factors the determine the amount of memory you can put in your system, the most prevalent of these is the motherboard chipset, the next being the BIOS.

Check if there is a BIOS update, its quite likely there simply is not a newer one. If there is, try it out, it may work. Even if it does however you will not see a full 4GB of ram in your system due the the reasons above.

Regards,
Jagannath
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