Upgrading existing VirtualBox VMs to 3.0 and multicore support 

A new version (3.0) of VirtualBox was released yesterday, finally adding SMP support. I immediately decided to try this feature out with some of my existing virtual machines, previously made in version 2.2.4 of VirtualBox. However, after setting my CPUs to 2 for a Windows Server 2003 machine, I noticed that, although in the Device Manager there were actually two cores available, only one was being used. Bummer #1.

After doing some research on the Internet, it turned that the HAL (Hardware Abstraction Layer) that was set on my VM was not the correct one. Bummer #2. And that, after more research, in order to replace the HAL on Windows Server 2003, I needed to do a repair install. Ouch, bummer #3. To cut a long story short, I wasn’t able to replace the HAL in a safe way (sure, there are other ways of replacing the HAL.dll on the system, but they appear way too risky to me).

So, how about a Windows Server 2008 box then? Well, initially you will see the two cores in the Device Manager, but only one is used. Again, HAL comes around the corner here. But this time, it was possible to change it, thank God! Thanks to this lenghty post, it was actually quite easy. Basically what you need to do is the following:

After the reboot you can clear the HAL detection if you want to. I did just to be safe.