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I have NVIDIA Quadro NVS 295 graphics card, asus P5B moherboard with 4GB memory, bios 2104, Intel Core 2 Duo E6300.

After inserting NVS 295 graphics, with 256MB, bios sees only 3,5 GB of memory (3584MB), the same issue was with NVS 300.

In bios I am using memory remap option to see whole memory in the OS.

Is there a way to get the memory back?

Explanation about the OS: it is 32bit, but with using PAE it has no problems with accessing more than 4GB of memory, so I do not blame the OS for losing the memory (I had whole 4GB before replacing graphics card to nvidia). I have two computers with exactly the same problem, one with 32bit Windows 7, and one with 32bit CentOS linux.

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Which operating system? 32 bit or 64 bit? –  ChrisF May 21 '12 at 8:41
    
@ChrisF - Based on the question he is using a 32-bit operating system. –  Ramhound May 21 '12 at 11:17
    
@Ramhound - that was my assumption too - but it was only an assumption. I left the comment so that the OP would improve the question. –  ChrisF May 21 '12 at 11:19
    
Can you be very specific about what OS you're using? Is it Windows? Linux? –  David Schwartz May 21 '12 at 11:34
    
Can you 100% confirm that with memory remapping on, the BIOS doesn't report all 4GB? Please triple check this. –  David Schwartz May 22 '12 at 0:25

2 Answers 2

If you have a 32-bit OS, turn memory remapping off. Otherwise, your BIOS will map memory where the OS can't access it. This will cause the BIOS to preserve as much usable RAM as possible, which is what you want for a 32-bit OS.

If you have a 64-bit OS, turn memory remapping on. Otherwise, your BIOS will not remap memory where the OS can access it. This will cause the BIOS to move as much RAM above the 4GB mark as possible. That's fine, since the OS can use all of it wherever it is. And that still leaves lots of empty space below 4GB for hardware mappings.

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Even if he does this Windows won't actually be able to use 4GB the very most he would be able to use is about 3.75GB because of the required hardware irq memory usage. –  Ramhound May 21 '12 at 11:20
    
It has nothing to do with Windows. It's the BIOS. With memory remapping off, the BIOS will not remap any memory above 4GB. Since some hardware mappings have to go below 4GB, even a 64-bit OS won't be able to access all 4GB of his RAM with memory remapping off. (However, if he has a 32-bit OS, this is what he wants.) –  David Schwartz May 21 '12 at 11:31
    
Memory remapping is ON, and I have the newest available BIOS version. I suspect that there is some bug in the motherboard, but I hope otherwise, that someone have found some method to fix it. –  Roman May 22 '12 at 13:12
    
And you are 100% sure the BIOS doesn't report all your RAM? –  David Schwartz May 22 '12 at 13:20
    
CPU-Z shows 4x1GB and the system BIOS have seen 4GB too before replacing graphics to Nvidia NVS 295, without memory remap it shows only 3GB. –  Roman May 22 '12 at 13:30

Use a 64 bits OS. A 32 bits OS assigns 32 bits addresses to all memory. That means you're limited to 2^32 = 4GB of memory, total. Since the videocard memory takes .5 GB, there are only 3.5 GB of addresses left for your 4GB of RAM. There's just no way in which you can (re)map 3.5 GB of addresses to 4GB of RAM.

This is called the pigeonhole principle. If you have 8 pigeons and 7 pigeonholes, you know that there is no way to assign each pigeon to a pigeonhole, even without trying.

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It is not an OS issue, the bios sees only 3.5GB, 64 OS will not help with that problem. Before changing graphics card I had whole 4GB of memory in the OS (now i have the same problem on two computers one with windows 7, one with linux). –  Roman May 21 '12 at 9:31
    
It is not true that 32bit OS can address only 4GB, pentium processor, since Pentium pro can address up to 64GB of memory. –  Roman May 21 '12 at 9:34
    
@Roman: That would be Address Window Extension (AWE) or PAE. Even then, you can assign only 4GB of addresses. However, you can change the assignment over time. –  MSalters May 21 '12 at 9:45
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The BIOS should not see the memory. Only when the BIOS sets up the mapping for a 64-bit OS will it see all the memory. You can tell the BIOS to set up for a 64-bit OS (by turning memory remapping ON) and then the BIOS will see the whole 4GB. But this will make less memory available to the OS, since the OS can't access remapped memory. –  David Schwartz May 21 '12 at 11:30
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If you have memory remapping on and the BIOS doesn't see all your physical memory, your BIOS (or your video card's BIOS) is borked. I'd suggest seeing if there are any updates available for your video card BIOS. (Also, see if the latest version of memtest86+ sees all the memory and can test it all. It definitely should.) –  David Schwartz May 22 '12 at 0:19

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