# Only reading 2.75gb ram when 4gb ram installed (ddr2)



## MR. NICE GUY (Mar 20, 2009)

Hi there, and thanks for your help ahead of time. I was running 64-bit Windows XP, and even 64-bit Vista for sometime, and never had any problems reading all of the memory (6GB with the 64-bit operating systems). But I ran into too many problems with drivers and software that I decided to switch back to 32-bit Windows XP Pro SP3 (until Windows 7 comes out).

The problem is, I currently have 4GB of RAM (two chips) but when I go to "system properties" under My Computer, it lists only 2.75 GB of RAM. I was under the impression 32-bit systems could handle up to 4GB of RAM. I just want to be able to utilize all 4GB. My system is as follows:

-XFX nForce 680i LT SLI motherboard

-Intel Core 2 Quad Q6600 at 2.40 GHz

-4GB DDR2 RAM (two 2GB chips running at 800MHz)

-GeForce 9600 GT 512MB GDDR3 graphics card

-solid 600watt power supply and proper cooling

I get the feeling that the video card may be drawing a lot of power or RAM from the system and I am 95% sure the RAM is not damaged, as only yesterday all 4GB would show up on my 64-bit version before I reformatted. Also before I reformatted, I cleared the CMOS, if you believe that may affect anything. Thanks for your help.


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## manic (Aug 2, 2005)

A 32 bit os can only see a hair over 3 gigs of ram. Maybe there is 
a limitation with the board, other than that, I dunno


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## Wrench97 (May 10, 2008)

32 bit systems can address up to 4gig including address space need for video and system devices, it will report anywhere from 2.6 to 3.5Gig as available memory most systems will show around 3.2Gig yours is in the lower end of the bracket but in the known range, if the bios shows 4gig as installed then the ram is good.


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## manic (Aug 2, 2005)

That clears up a few questions I had about ram in 32bit os's..
Thanks, Wrench,,:grin:


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## MR. NICE GUY (Mar 20, 2009)

Thanks for the help. I suppose since I am running a high-end video card it's just pulling a lot more juice from the RAM? I don't even understand what that means if someone could explain.

Is there a diagnostic program anyone knows of that tells you what your running, and at what speeds, temps, that kind of stuff?

Thanks for your help.


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## Wrench97 (May 10, 2008)

CPUz will give you ram and cpu speeds as well as brand and model info > CPUz

GPUz will give you video card data> http://www.techpowerup.com/downloads/1207/TechPowerUp_GPU-Z_v0.2.8.html

The Bios is the most accurate for voltages and temps, but CoreTemp does a good job on Core Duos and Amd cpu's > http://www.alcpu.com/CoreTemp/

It;s not that the video card is taking power from the ram it's taking address space from a limited number of address 32bit os's are limited to 4Gig total address space Nvidia boards seem to reserve more address space then other chipsets it might have to do with the mcp chip being the same as used on integrated video boards reserving more address space then really needed, not sure just an observation, 64 bit also has a limit theoretically of 120Gig, at the moment that seems like a number we'll never see just like 4Gig did when 32bit came out in 1995 and everybody said what are you going to do with 32meg of ram installed?


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## Stu_computer (Jul 7, 2005)

All 32bit CPU's for the past decade (since pentium pro) are capable of working with up to 64GB of ram.

On Windows 32bit systems the 4GB barrier is not a CPU or chipset limitation, it's because the I/O devices can't access above 4GB of ram.

For example, the PCI bus uses *Direct Memory Addressing* (DMA) which allows a PCI device to read/write directly to ram--thus freeing up the CPU. Since the PCI bus is 32 bit it can only *directly* address up to 4GB of ram.
So, Windows 32bit versions are limited to 4GB to avoid memory problems, (exception is windows 32bit server versions can be greater than 4GB for the applications to use).



Here is a simple visual example of how the ram is used....

RAM____________________Up to 4GB maximum with XP32

*XP loads at top address*
system will allocate itself up to 2GB if enough ram installed

(bottom of OS partition)
=======================
(top of processes partition)

memory space for programs (up to ~ 2GB if enough ram installed)

may also be used by chipset for additional I/O (ie: video)

----------------------(low memory address)
*I/O devices* (reserved addresses)

(ie: video, PCI, mouse, kybd)
_______________________zero



Now, with 64bit systems all PCI devices must be PCI 2.1 compliant to access above 4GB.

That means a PCI 32bit device must support PCI 2.1 *Dual Address Cycle* (DAC) for it to access higher than 4GB on a 64bit system.

So, if you use older PCI 32 bit cards make sure they are PCI 2.1 compliant and the proper driver is used--check manufacturer site for newest drivers--else the card may cause a memory problem for 64bit systems.


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## Gfx010 (Jul 25, 2009)

Stu_computer said:


> So, if you use older PCI 32 bit cards make sure they are PCI 2.1 compliant and the proper driver is used--check manufacturer site for newest drivers--else the card may cause a memory problem for 64bit systems.


How can I know which if my PCI is PCI 2.1 compliant ?


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