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When is 4Gb of RAM not 4Gb?


Established Member
Hi all, just upgraded the memory in my PC and not getting the results I was expecting, hope someone can give me some insight into the problem..

I have an Hp xw6200 workstation running XP professional which up until about 30mins had 3Gb of PC2-3200 RAM fitted (2 x 1Gb, 2 x 512Mb). Going to My Computer/Properties showed 3Gb total as expected. I then removed the 2 x 512Mb and replaced with 2 x 1Gb and re-started. The boot up screen showed a new configuration of 4096Mb (4Gb) of RAM, but My Computer only shows 3.25Gb, so I ran SiSoft Sandra and that reports that I have 4 banks of 1Gb memory but the total is only 3.25Gb. I would like to add that all the RAM fitted is HP approved and although by different manufacturers is identical in specification.

The following is from SiSoft Sandra:

System Memory Controller
Location : Mainboard
Error Correction Capability : m-bit ECC
Number of Memory Slots : 4
Maximum Installable Memory : 8GB
Bank 1 - DIMM1 : JEDEC ID:7F 7F 7F 7F 7F 51 00 00 72T128000HR5A 12520D05 DIMM Synchronous DDR2-SDRAM 1GB/72 @ 400Mt/s
Bank 2 - DIMM2 : Micron 18HTF12872Y-40EB3 BDD404D7 DIMM Synchronous DDR2-SDRAM 1GB/72 @ 400Mt/s
Bank 3 - DIMM3 : Hyundai Electronics HYMP512R72P4-E3 39320000 DIMM Synchronous DDR2-SDRAM 1GB/72 @ 400Mt/s
Bank 4 - DIMM4 : Hyundai Electronics HYMP512R72P4-E3 31320000 DIMM Synchronous DDR2-SDRAM 1GB/72 @ 400Mt/s

Looks to me as though their is 4Gb there, is this just a reporting error (hope so!)? Any coments on this very welcome!


Established Member
I had the same issue with my Vista machine and my XP machine. It seems that there is a limitation on the amount of RAM your system can actually make use of. In my case it was limited by the Motherboard which only supported up to 3.25 GB RAM.

This may not apply to your machine, but the symptoms are the same. I would see 4GB of RAM during boot, but once the machine was up and running the RAM only ever registered as 3.25.

My iMac, on the other hand had 1GB initially which I upgraded to 4GB, in this case all 4GB is available and reporting and being used properly.

I guess it's like all computer stuff, i.e. perhaps there is a virtual bottleneck in your system that is preventing all 4GB from being used.


Established Member
First moriartygm, thanks for the ultra quick reply - :clap:

Would agree with you but the motherboard should be capable of taking 8Gb....glad I didn't spend £££££££££££££ and fit 4 x 2Gb modules only to gain 0.25Gb!

At the end of the day I got the memory off of fleabay so haven't lost much.

Any other comments, is there anything I can do to release the extra RAM?


Established Member
Well, I don't really know because I gave up Widows PC's at around this time. I was so frustrated by Vista that first I 'upgraded back to XP' and then I went and switched to iMac. Windows PC's now live in the attic.
I seem to remember it has something to do with a RAM header setting that was limiting the systems to 3.25, even though the Motherboard, in theory, should have accepted it. This was just one of the factors that drove me away from PC's.
Try a google search for 'RAM header' or 'RAM limit 'perhaps there is something you can do. I remember that I gave up on the idea though, it was just to much of a problem to solve for me.

Paul Shirley

Established Member
Any other comments, is there anything I can do to release the extra RAM?
Install a 64bit oS.

32 bits covers a 4Gbyte address range, some of which is occupied by hardware in your PC, leaving (in your case) 3.25Gb available for RAM. While there are ways to configure a CPU to access all 4Gb they aren't used (or very useful in any case). A 64bit OS doesn't have that limit.


Established Member
Ah, yes, this is coming back to me now, Paul is quite right, I was using Vista 64 bit and encountered this as he has described. Thanks for jogging memory !


Standard Member
install a 64bit os.

32 bits covers a 4gbyte address range, some of which is occupied by hardware in your pc, leaving (in your case) 3.25gb available for ram. While there are ways to configure a cpu to access all 4gb they aren't used (or very useful in any case). A 64bit os doesn't have that limit.



Established Member
Done a bit of digging myself and as you all rightly say it is because I am running 32 bit XP, not 64 bit. Wish I had known this before I had shelled out for the extra RAM :mad:

Thanks for all your replies, think this is the quickest responses I've ever had :clap::clap:

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