[Updated with Mac OS versions. See footnote 3.]
I’m glad Windows 8 is named the way it is. With Windows 7 Microsoft went to a numbering system which is much more rational than the mixed naming of the past. The number 8 actually corresponds to the actual sequential number of major versions of Windows released to date.
Windows proper actually did not start with what was called “Windows 1.0”. Windows actually started in April 1992 when Windows 3.1 was released. It was the first Windows which was an operating environment onto itself, apart from DOS. It was followed by Windows 95 (which we can call “2”), Windows 98 (“3”), Windows 2000 (“4”), Windows XP (“5”), Windows Vista (“6”), Windows 7 and now Windows 8.
Given this nomenclature and the dates of general availability of said versions, we can derive a measure of the frequency of upgrades. For example Windows “2” followed about 41 months after “1” and “3” took 34 months after “2”. If we continue this for all the versions, and assume “8” will launch by October next year, we can plot the cycle times of new Windows versions.
To make the story more interesting I added the same data for other OS platforms. OS X, iOS and Android have version numbers which correspond to the sequential order in which they were released. I am assuming that the numbering system (1.0, 2.0, 3.0 etc.) are meaningful and that major releases are given a new integer value.