The Project VRC (Virtual Reality Check) Phase III whitepaper has been released. As more and more companies move to a VDI deployment, performance and sizing issues are still a major hurdle to overcome. Often, VDI results are disappointing because the VDI environment is not properly sized and tuned. In practice, storage remains the number one challenge in today’s VDI deployments. In this whitepaper Windows XP and Windows 7 are extensively compared. Specifically, the I/O behavior of Windows XP and Windows 7 is investigated in detail. By evaluating the different phases of a desktop workload, completely new insights are given. Many best practices are available to optimize Windows 7. Project VRC performed tests with the default optimizations configured by VSI (referred in this document as ‘VSI optimizations’) and additional optimization best practices that are specific to Windows 7 (referred as ‘VRC optimizations’). Both from an I/O and VSImax (maximum capacity) perspective, these ‘VRC optimizations’ proved to have a significant positive impact. Project VRC also investigated the performance impact of topics like ‘Page file configuration’, ‘Address Space Layout Randomization’, ‘VM logging’, ‘ESXTOP’, ‘1 vs 2 vCPU’s’, ‘ESX 4.0u2 vs ESX 4.1’, and ‘Overcommitting Memory’. There are many lessons to be learned here, but the impact of disabling ASLR was striking. It is difficult to blindly recommend disabling such an important security feature, but the impact is large enough to consider it. All tests were performed with either vSphere 4.0 U2 or 4.1 as the hypervisor and all VDI tests were performed using View 4.0. Apart from specific recommendations for vSphere, all Windows related conclusions are valid for any kind of hypervisor or VDI solution.