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Why am I only seeing 2.5GB when I have 4GB's?


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I just built this system yesterday and it seems to run fine.

However when I was looking at my system properties:



I only see 2.50GB of memory!? I'm suppose to have 4GB of memory!?

(I know with Win XP 32bit, I'm only suppose to see 3.5GB)


It appears that one of my memory sticks is bad?

So what & how do I check the memory?

I have them installed in DIMM Slot 2 & 3 which the manual says is OK.

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Let me clarify.


Your computer has many methods in which to use memory. There are memory storage and caches all over the motherboard. These devices contain some of the below method of storage:




* Cache

* Dynamic RAM

* Static RAM

* Flash memory

* Virtual memory

* Video memory




For example, your sound, video, keyboard, chipset caches, I/O controller (IDE, SATA, etc) caches . . . Now these device with discrete and cache RAM need to have their "Addresses" so that the computer knows where they are in order to query and access them.


You computer also has System Resource Memory. Consider this as an index of addresses that tell the computer where everything is for access as mentioned above. The computer needs to know that a certain boundary of addresses will contain certain functions to perform when commanded.


Memory-mapped devices (such as your video card) will use some of that physical address space, as will the BIOS ROMs. After all the non-memory devices have had their say, there will be less than 4GB of address space available for RAM below the 4GB physical address boundary. Now a 32bit Operating system such as Windows XP 32bit and VISTA 32bit have the ability to access 2^32 bits = 4GB. Now if you have an 8800GTX with 768MB of DRAM, then that memory must be addressed in the space of the 4GB and you lose some of the system dram to the addressing. This continues with all other devices, leaving you with less than the 4GB. Since Windows can address up to 4GB, then with 3GB, there will be the 3 --> 4GB mapping so you should not lose that DRAM with 3GB unless your devices demand it. As with your system, SLi with 2 X 8800GTS 7512MB will certainly take away from the 3GB. Remove one card and see. My advice? Buy a 64bit OS.


If you had a 2 GB system, then the addressing is done in the discrete video card DRAM.


In your system, the Video card ROM is accessed by the CPU and 1.5GB of DRAM is seen. There is no addressable space since you are at the 4GB plateau level. Thus the CPU reserves 1.5GB of that 4GB. In a 64bit OS, the 4GB is like the 2GB is in a 32bit OS and the CPU just addresses the Video cards discrete DRAM above the 4GB level. On a 64bit OS with 8GB, the Video cards discrete DRAM is addressed above the 8GB.

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I can't believe this. I'm virtually wasting 1.5 of my 2GB memory!!!

I pulled each stick and ran one. They both worked. They both read 2GB's in system properties.

Then when I put them both back in, system properties said 2.5GB. What a CROCK and a waste of money.

See attached screenshots.


Would XP Pro 32bit improve on that or am I forced to spend $150 just to get a new XP Pro 64bit?





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No 32bit OS will be able to allow you the full use of your 4GB. You must transition to a 64bit OS.
I understand that.

I understood before I posted that 32bit couldn't use all of the 4GB. I was use to seeing 3.4GB or with 32bit, so and that didn't bother me at all. What bothered me is seeing only 2.5GB out of 4GB's. I haven't seen that before and there are some people here running 2 graphic cards and still seeing 3.4GB in system properties.


I'm just wondering if there are some settings in BIOS that would affect it as I see that EVGA 780i has tons of changes that can be made in BIOS.


I will probably sell my unused XP Pro and get the 64bit version. I may even consider Vista 64bit, but I'm still leary of Vista.

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