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4 GB of Ram installed but only 2.97GB usable. What gives?

I've just taken an existing XP Pro 32 bit system that had only 0.5GB of memory installed and maxed it out to 4GB.

The BIOS reports the 4GB ram however when XP is booted and I look at the computer properties only 2GB of RAM is reported. Can anyone explain this?

Before we go up any blind allys the /3GB switch is not the answer here, I have no need for a single process to use more the 2GB of memory.

I'm wondering if the the 32 bit XP Pro is deliberately limited to 2GB. I seem to remember seeing an excellent table on a Microsoft site listing all the various SKUs of Windows and what each one was limited to. However I can't seem to find that table now.

Edit: Motherboard info.

The motherboard is a Asus A8N-VM. According to the manual it will accept up to 4GB of mem.

Edit 2:

Well it would seem I've also got a similar problem as reported by this question Windows only sees 768 MB RAM out of 4 GB. In my case the PCI Bus seems to have allocated memory from 0x7800000 all the way to the top, even though the first device inside the connection is the NVidia 6100 starting a 0xD0000000. The difference is the missing 1GB or so.

I have no idea how to convince the PCI Bus to not start its allocation so early.

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migrated from May 15 '10 at 17:11

This question came from our site for system and network administrators.

marked as duplicate by Sathya, ChrisF, heavyd, Phoshi, Ivo Flipse May 18 '10 at 12:55

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

@Sathya: Thanks for that set but none of them address the question at hand. In fact Windows is reporting 1.93GB, I can grasp it not reporting all of the 4GB but 1.93GB is a big drop from 4. – AnthonyWJones May 15 '10 at 19:15
Do You have a 1GB graphics card? – Nifle May 15 '10 at 23:07
@Anothony wrt Edit 2: check your BIOS, there should be an option to alter the mapping. A BIOS update might help. – Sathya May 16 '10 at 4:31
@Nifle: The Graphics are on board and is set to 128MB, so I'd expect to loose at least that and then some. I fully expect to loose a good 700MB of it but not 2.7GB of it as I currently seem to be. – AnthonyWJones May 16 '10 at 8:29

Check the web site of your mainboard manufacturer, some chipsets have hard limits, specially if they are old.

Another possibility (unlikely however for a system that was originally 512Mb) is a graphic card with too much memory.

Have also a look at this :

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Thanks for you response, I did check that the motherboard would accept the memory and as I stated in the question the BIOS reports the full 4GB. – AnthonyWJones May 15 '10 at 20:39
+1. It would seem I am suffering a similar issue. – AnthonyWJones May 15 '10 at 21:03

This page says 4GB, so it's probably not the SKU.

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Thanks that was the table I was looking for. I was kinda hoping that it would be the answer. So I'm still no wiser to why I'm not seeing memory closer the 4GB being reported. – AnthonyWJones May 15 '10 at 19:17

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