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I have installed Windows Server 2008R2 and now trying to install multiple Windows Server 2008R2 as guest. My CPU is Intel Core 2 Quad Q8400 @ 2.66GHz on Asus P5P41T-LE mainboard. First I have to tell there is no place in BIOS to enable Intel VT-x. Intel web site says this CPU supports VT-x. When installing guests, VirtualBox says:

attempting to load a 64-bit application however this cpu is not compatible with 64-bit mode

But Hyper-V can load 64 bit guest with no problem. I have tested my CPU with Securable tool. It says my CPU does not support VT-x. The question is WTF is happening? Are there two editions of Q8400 with/without VT-x?

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The 8400 should have VT-x but it is missing VT-d. So it should be working perfectly fine. Have you stopped Hyper-V and it's related services before starting VirtualBox? Running multiple VM softwares at once can cause bad things to happen (usually instability of the host) –  Justin Nov 27 '12 at 12:24
    
Yes I have checked VirtualBox before starting Hyper-V services. –  Majid Azimi Nov 27 '12 at 12:56
    
This sounds like a problem with Virtual Box does VMWare have this problem? This will require running the Hyper-V Services. –  Ramhound Nov 27 '12 at 13:09

1 Answer 1

I just had the same problem with Hyper-V being able to host 64bit systems, while on the same machine VirtualBox wasn't. The issue is that the Hyper-V service occupies VT-X right after startup, hence no other service (like VirtualBox) can claim it.

The only way I found to resolve the issue was by completely removing the entire Hyper-V feature through the windows feature settings an rebooting. After that VirtualBox was able to host 64bit systems.

See see this answer on how to turn Hyper-V on and off, without having to remove the feature completely.

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