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I ordered a new computer with 8GB RAM with the plan to run Windows 7, 64Bit. Turns out now, that I need to run a 32Bit OS (XP or 7) due to some software which does not run on 64Bit yet (not even with any of the available compatibility settings / modes).

Is there anything I can do with the memory above 4GB in this scenario? I'm willing to consider creative solutions like running a hypervisor under XP that offers the memory as a RAM-Disk for swapping etc. ?

The software that does not run on 64Bit is CISCO VPN (there seems to be a half-working solution for that) and CISCO IP phone / webcam integration "CISCO Unified Video Advantage" (there is apparently no solution for that).

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If it weren't for the fact that it's VPN software I would have suggested that you install Windows 7 64bit, install Windows XP Mode, and run your incompatible software in Windows XP Mode. –  joeqwerty May 6 '10 at 0:14
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6 Answers

I'd recommend going ahead and installing Windows 7 64-bit, and running your Cisco software in a VM.

Edit: I just noticed joeqwerty pointed out that Windows XP Mode might not work very well for VPN software. I'm not familiar enough with Windows XP Mode to know why this would be a problem, but you could still use a different virtualization platform, such as VMware or VirtualBox.

For example, you could use VMware Server to install a 32-bit Windows XP virtual machine, and configure that VM to start up every time your computer boots up. As long as you configure the network adapter as a bridged network adapter, the VPN software should be able to route traffic between the local network and remote hosts, just as it would if it was installed on a physical machine.

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I think a VM is the way to go here. –  WindowsEscapist Dec 20 '12 at 2:52
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Install Windows 7 x64. Use Shrew to connect to your VPN. Use Windows XP Mode for your communicator software.

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If you have the licenses to support it, I highly recommend that you run windows 7 x64 or Linux x64, install virtualbox, and run your 32 bit OS as a guest. Once the software becomes 64 bit compatible you can ditch the guest and just install it on the main host.

If you are dead set on making this work, and you are a badass, you can hexedit the windows 32 bit kernel to enable "physical address extensions". This will allow you to use all of your RAM. Yes, it's that easy.

There is a very detailed guide here at the evga forums.

Hex editing is not hard. The guide looks like it takes 45 mins. Someone also claims you can create a ramdisk with the additional ram and put the page file on it, in effect giving the additional ram use through the paging layer.

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Looks cool. Unfortunately, well fortunately really, I have since moved on from that machine and can no longer try it. If anybody else can independently verify it works I'm happy to accept it as answer. –  user12889 Dec 20 '12 at 4:01
    
Haha, no idea I resurrected an old question. I wonder how it bubbled to the top. –  khaki54 Dec 20 '12 at 4:07
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Unfortunately neither Windows XP SP2 32-bit nor Windows 7 32-bit support more than 4GB of physical memory. You'll need to switch to non-trivial variants of Windows Server 2003 or 2008 (or something non-Windows) in order to use all physical memory.

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Both XP and Windows 7 can technically address more than 4 GB of memory. The 4 GB limit is just a licensing restriction: geoffchappell.com/notes/windows/license/memory.htm –  RoadWarrior Sep 3 '12 at 11:03
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You could use the remaining memory as a RAM Disk: http://www.superspeed.com/ramdisk.php

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Nothing there implies "works with physical memory the OS can't get to". –  Ignacio Vazquez-Abrams May 6 '10 at 3:26
    
@Ignacio : Another user of SU uses this software, I can't seem to find the comment I posted to him. –  Sathya May 6 '10 at 14:44
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This question was asked before and Microsoft decided that 4GB is enough for 32bit XP:

http://superuser.com/questions/67444/67596#67596

You could run XP 32bit in a VM, but I don't know if that would be a good solution for you. Although, you can always dual-boot. This way you can get the best of both worlds.

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"Microsoft decided"? NO. It has to do with the fact that a 32-bit pointer can only access $2^32$ bytes. i.e. 4GiB. –  Cole Johnson Dec 20 '12 at 2:52
    
This is partly true - with PAE you can address more than 4GB. The simple fact that Microsoft limited 32bit Windows to 4GB is a license issue not a technical one. Microsoft supports PAE on their Windows Server platform see this link - msdn.microsoft.com/en-gb/library/aa366778%28VS.85%29.aspx . Windows Server 2003 R2 Enterprise x86 supports up to 64GB of RAM. –  Nathan Adams Dec 20 '12 at 6:35
    
In fact PAE is bundled with the Linux kernel - so if you have more than 4GB running a 32bit Linux distro it may automatically detect this and switch to a PAE enabled kernel which will result the ability to use more than 4GB in a system. See here for Ubuntu help.ubuntu.com/community/EnablingPAE –  Nathan Adams Dec 20 '12 at 6:39
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