With all the recent extensive delays in the development of Windows Vista, and growing concern at what compelling new features it will offer over the ageing XP, it strikes me as a suprise that Microsoft hasn't dropped support for 32-bit processors with Windows Vista. Think of it this way, if Microsoft didn't make a 32-bit version: - You could potentially shave about 6 months off the development time, if not more - Hardware/software vendors would have a single platform to develop drivers on. What I can see happening, it that vendors may decide there isn't a large enough audience running the 64-bit version of Vista, and you'll have the same situation as you have now with Windows XP x64 with regards to drivers and software. - Compatibility would still be maintained with 'legacy' 32-bit apps similarly to the way it has been in XP x64 - As all Vista apps would be 64-bit, the system performance increase would be substantially greater - People would stand up and take notice: "Wow, this only works on 64-bit computers, it is actually something new." The only downside I can see is on the laptop front - only AMD64 and yet-unreleased Merom-based laptops could run it, however, pretty much only AMD64 and Merom based laptops would have the required performance for the full ‘Vista experience’. I cannot see a commercial disadvantage either – most personal and business users upgrade their operating systems with hardware, so 64-bit support won’t be a problem. Software Assurance customers will still be paying their annual subscription fees aswell.