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Is it possible to run a 64 bit guest OS inside a 32 bit Windows 2003 host OS? If yes, which virtualization products support it?

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I run a 64bit Windows 7 Enterprise on a 32bit Windows XP Pro host using VirtualBox for testing purposes. Works perfectly. The processor needs to be 64bit capable and support VTX for it to work though.

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And I did the same with 64 bit Server 2008 on 32 bit XP. Not real fast but perfectly workable for testing. – John Gardeniers Mar 2 '10 at 12:01
I've done similar with VMWare too. I think it is required that your CPU supports AMD-V or Intel's VT-x for 64 bit guests to function on 32-bit hosts. Performance should be similar to 32-bit guests (unless your 64-bit setup requires more RAM to be allocated, of course). – David Spillett Mar 3 '10 at 13:21

As long as your hardware is 64 bit capable, it is possible (the OS does not need to be 64 bit).

Also, it is certainly possible to emulate a 64 bit machine in a 32 bit machine (32 bit CPU).

To @Saronthe's point, you probably don't want to.

This thread might help clarify some of the issues:

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The hardware needs to support paravirtualization aswell, on order to support 64-bit guests natively (without emulation) – jishi Mar 2 '10 at 7:42
Actually, it does only if you want to run guests that aren't aware of being virtualized. A Xen-aware guest runs just fine in my non-AMD-V AMD64-3000, and that's paravirtualized. – quadruplebucky Mar 2 '10 at 12:45

Not sure if its still supported but VMWare certainly used to support this providing your processor had the hardware support for virtualisation.

The virtualised guest's processor instructions are interpreted directly by the physical processor when the processor supports hardware VT, so there's no inherent technical reason why the guest and host have to be the same at this point.

I still feel it is probably neater and simpler just to have a 64-bit host these days to solve things like memory use, but it seems like VMWare, at least, are willing to at least have a go for you.

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VirtualBox supports 64 bit guests on 32 bit hosts, with the following stipulations:

Starting with Version 2.1, you can even run 64-bit guests on a 32-bit host operating system, so long as you have sufficient hardware.

In particular, 64-bit guests are supported under the following conditions:

  1. You need a 64-bit processor with hardware virtualization support
  2. You must enable hardware virtualization for the particular VM for which you want 64-bit support; software virtualization is not supported for 64-bit VMs.
  3. If you want to use 64-bit guest support on a 32-bit host operating system, you must also select a 64-bit operating system for the particular VM. Since supporting 64 bits on 32-bit hosts incurs additional overhead, VirtualBox only enables this support upon explicit request.
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It may not be possible. The 64bit OS's expect a different instruction set to the legacy 32bit OS. Unless the guest is being emulated, and every CPU operation being executed via emulation, then this will likely fail to work at all once the CPU, in 32bit mode, hits a 64bit instruction.

If you're host CPU is actually 64 bit capable, it is likely that the UI inside VMWare, or similar virtualisation products, will prevent you event from doing this.

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The real CPU will not encounter any "64bit instructions" for a processor it is emulating. – quadruplebucky Mar 2 '10 at 6:47

Putting a 64-bit guest on a 32-bit host completely defeats the purpose of a 64-bit guest. There is no reason to provide anyone with a "64-bit OS" under that circumstance.

I suggest you review

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It may not be a "best practice", but at least you have to try. My previous employer used to provide laptops with 32bit OS only, but that didn't stop me from running x64 Linux and Windows to run tests on virtual machines. – Luis Ventura Mar 2 '10 at 7:45
@Sanarothe - Testing code and applications without needing a 2nd physical test machine isn't a reason? I suggest you keep the condescending links and opinion to yourself and stick to answering the questions until you have a little more rep and know how things work around here. – MDMarra Mar 2 '10 at 8:23

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