VirtualBox for Ubuntu (64-bit) is a cross-platform virtualization application. Which means it installs on your existing Intel or AMD-based computers, whether they are running Windows, Mac, Linux or Solaris operating systems. Secondly, it extends the capabilities of your existing computer so that it can run multiple operating systems (inside multiple virtual machines) at the same time. So, for example, you can run Windows and Linux on your Mac, run Windows Server 2008 on your Linux server, run Linux on your Windows PC, and so on, all alongside your existing applications. You can install and run as many virtual machines as you like, the only practical limits are disk space and memory.
Version 4.2.12 has fixed a Guru Meditation on putting Linux guest CPU online if nested paging is disabled and added handle fall-back to VESA driver on RedHat-based guests if vboxvideo cannot be loaded.