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[help] Windows XP sp2 4 GB of RAM


D8TA

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I just added 4 GB to my Dell GX280 Windows XP sp2 PC but it appears the PC only sees 3GB. I've tried the /3GB and /PAE on the boot.ini file but one, both, or the other just blue screens and restarts. I read on Techne where Windows XP supports 4GB so is there some other switch I need to use or what else do I need to do so my PC will see this other 1GB of RAM. I have 4 - 1GB sticks all the same and the system properties shows up as 2.99GB.

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Your hardware uses certain address ranges and take from the 4gb

A 32-bit Microsoft desktop operating system will NEVER see 4gb of memory to the system; thats the design and its limitations.

If I understand this correctly, Windows programs can use only up to 3 GBs of the RAM, but the remaning 1 GB isn't left unused - it is used by the system/kernel... If the original poster is using WinXP Home though, it would be better to try Pro instead.

Edited by Naki
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Your hardware uses certain address ranges and take from the 4gb

A 32-bit Microsoft desktop operating system will NEVER see 4gb of memory to the system; thats the design and its limitations.

If I understand this correctly, Windows programs can use only up to 3 GBs of the RAM, but the remaning 1 GB isn't left unused - it is used by the system/kernel... If the original poster is using WinXP Home though, it would be better to try Pro instead.

You're confusing virtual addresses with physical addresses.

Virtual addresses beyond 3Gb (C0000000) are indeed used by the system drivers and ring0 components.

Physical addresses, 3-4Gb are also 'reserved' and devoid of any actual RAM, as mmio ports and other things lurk here.

With PAE enabled, the physical addresses beyond 4Gb can also be used for physical RAM.

Also, don't forget that your processor has to support PAE. This is supported on all CPUs starting from the Pentium Pro, so that point is moot.

Ensure that "Physical Address Extension" is displayed in the System Properties dialog below the amount of RAM the system can sense. If it doesn't mention PAE, then it's not enabled.

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I am using Windows XPsp2 Pro and in the System Properties dialog box it does say Physical Address Extension. So even though it says 2.99GB I am using all 4 GB of RAM?

I was wondering if it wouldn't be better to re-image my PC and use Windows Server R2.

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What is basically happening is that your system's BIOS has reserved memory for the PCI bus, a PCI-x or PCI Express bus, and other system components. It then reports to Windows that the 4GB boundary is actually lower that 4GB so that Windows doesn't attempt to use the reserved RAM (you will probably see all 4GB of RAM if you run msinfo32).

Note that even after adding the /PAE switch, you won't see anything more than ~3GB of RAM, because the BIOS has told Windows that the 4GB limit is not at FFFFFFFF, but lower. Unless you have an OS that can see above 4GB of RAM (x64 versions of Windows, 2000 Advanced Server, or Server 2003 Enterprise), you will still not see any more than 3GB.

If you do start > run and type msinfo32 and click OK, the system will do a WMI check on the installed memory (not available, but installed) - and assuming your BIOS indeed sees all 4GB installed, you'll see ~4GB of RAM in the msinfo32 report.

There's not much you can do other than run an x64 OS, or install a version of Windows that can actually use the /PAE switch to see more than 4GB of RAM if you want to use it all. It's not a Windows problem, it's a BIOS issue.

And please don't use the /3GB switch unless you have applications that can use more than 2GB of virtual address space - you're hamstringing your kernel into 1GB of address space, and that's not a good idea unless you need to do so.

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