For a time, there was a release named Windows Installer 4.1 on the MSDN topic Released Versions of Windows Installer that was associated with Windows Vista SP1 and Windows Server 2008. When this reference to 4.1 was removed, it naturally lead to the question: what happened to Windows Installer 4.1?
The back story here starts about this time last year when we were finishing up Windows Installer 4.0 in Windows Vista and asking ourselves "What's next?". At that time, we didn't know the bar for features in Windows Vista SP1 and next major release of Windows. For those of you watching Microsoft closely at the time, you may recall this is when there was a lot of change going on in the upper echelons of Windows
We also had the seeds of an out of band release germinating in the organization.
In this fluid context, we had to figure out names for what appeared to be three simultaneous efforts from the Windows Installer team. Knowing none of the feature and release criteria, our best guess at the time was that Windows Vista SP1 would ship first, an out of band release would ship next, and then the next full version of Windows would be our focus. With this guess at timelines, we chose the names Windows Installer 4.1, Windows Installer 4.5, and Windows Installer 5.0 as the labels for the next three buckets of work from the Windows Installer team.
It just so happened that at this same time, the Windows Vista version of the Platform SDK was finishing up. Given our best guess was that we'd be doing significant work in Windows Vista SP1, we added the reference to Windows Installer 4.1 for anticipatory completeness.
What changed was that the new guard in Windows had a very different bar for the Vista SP than had been in practice for previous releases (at least in my memory). Generally there is lip service to no large feature work in a SP but this time folks listened. Big feature adds were heavily scrutinized. The items we wanted to fix in the SP, UAC tweaks, were big feature by the new bar.
When the UAC tweaks were rejected for Vista SP1, the justification for 4.1 faded as there were no new features in the Windows Installer in Vista SP1.
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