Wow if I thought you were talking in total on different machines that I've owned and used over the years, I would have clicked 10 or more.
I clicked on 9 just for Win XP PRO.
I have had Windows from version 3.11 onwards, so that would have been 4 installs, moved on to Win95 x2, 98 x2, 98SE x4, W2K x3, 2000 PRO, XP and then XP PRO x 9.
That doesn't include drives dying and formatting to reinstall, mainly XP.
Hmmm I wonder if that's a Windows fault .... maybe the user.
Oh and for those that might ask... Yes they are all legal copies.. Hahaha