Microsoft: Windows 7 upgrade can take nearly a day
While developing Windows 7, Microsoft ran many different performance tests to make sure the operating system was an improvement over its predecessors. One of the tests focused on upgrade performance: Microsoft wanted to make sure that an upgrade from Vista SP1 to Windows 7 was within a five percent threshold faster than an upgrade from Vista SP1 to Vista SP1. Microsoft gave three reasons for using the Vista SP1 to Vista SP1 upgrade as a baseline instead of Windows XP to Vista: