In this post I am taking a different tack to write about my perspective on the underlying causes of the Windows Vista codename Longhorn debacle. While this happened over a decade ago, this was a crucial period in the shift to mobile and had long-running consequences internally to Microsoft. I think there is a different story to tell — one that is better rooted in the actual facts of the projects and the real motivations of key parties. This is not an effort at alternative history — I have no idea what would have happened if these mistakes were not made but they certainly did not help Microsoft navigate this critical inflection point in the computing industry. This is also not investigative journalism — I have not done a deep series of interviews with key parties. This is my point of view based on what I experienced during that period and learned afterwards. Although I was in the Office organization at the time, I worked closely with many Windows partners and so was very aware of what was happening in the Windows organization. I apologize for the length. The TL;DR; version is: Microsoft badly misjudged the underlying trends in computer hardware, in particular the right turn that occurred in to the trend of rapid improvements in single-threaded processor speed and matching improvements in other core elements of the PC. Vista was planned for and built for hardware that did not exist.