What version was installed? x64 or i686? What's the difference exactly?

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http://askubuntu.com – Okay, so heres my problem. I recently started migrating several services to individual VMs on my box, using VirtualBox 4.1. I created a new VirtualBox VM with guest type "Ubuntu (64 Bit)". I've already done this before and it worked like a charm. I then installed unbutu server (12.04) from the exact same dvd image. All the time I thought that it should have installed x64. I already put a few hours work into the new VM, migrating the webserver and mail system etc. Today I tried installing a x64 piece of software and it suddenly told me that it needed x64 and I had only i686. I checked uname (HowTos)