Virtualization is a very popular Operating System add-on these days. Machine Virtualization, such as that provided by VMware and Microsoft Hyper-V, augments the OS with virtualization from the outside. Application Virtualization, such as that provided by Microsoft App-V and VMware ThinApp, augments the OS with virtualization from the inside. With all this augmentation going on, it’s worth remembering that most OSs have quite a bit of virtualization built-in. I’ve already written about the virtualization built into Vista. A recent post by Microsoft’s Raymond Chen mentions another such built-in virtualization: 32-bit OS virtualization in Windows x64 (Raymond must have missed all the hoopla in the press about virtualization because he insists on calling this technology “emulation”).