​What are virtualization extensions?

In computing, virtualization is used to create a simulated, or virtual, computer within a host computer. For example, if you have a PC running Windows 7, virtualization allows you to run a Linux operating system (OS) without having to get another physical machine on which to host a different OS.

Since virtualized computers necessarily run in software (and the software runs within the operating system of the host machine), the performance of the virtualized OS, and any software running in that environment, will be slightly less than it would be running on the OS of the physical host machine.

To help improve the performance of virtualized environments, some central processing unit (CPU) manufacturers offer hardware-assisted virtualization. This feature allows a virtualized environment to access CPU resources directly, rather than doing so through the host OS. This feature improves the performance of the virtualized OS.
How can I find if my CPU supports virtualization extensions?

Load up your BIOS settings, and look for AMD or Intel Virtualization settings. If they are present, enable them. Your OS will now be able to use the CPU's virtualization extensions.

Where can I buy a computer that has Virtualization extensions?

Most new laptop and desktop CPUs support this feature, but to be sure, look up the model number and look here for Intel and here for AMD. Intel will have VT-x and AMD will have AMD-V​ extensions.