I've learned a few surprising things about Windows that I thought I'd share with the list.
Computer: Dell Inspiron 1501 with Windows Vista (on which I'm installing Buster but want to keep Windows to update my Garmin GPS once or twice a year). When I was booted into Windows (Vista) on this machine, I found that the Windows partition was being filled up with something (free space decreased from about 2 GB to almost nothing) while I was getting ready to download and install the Garmin update software. I eventually realized that, apparently, Windows was downloading files in order to update itself (maybe even to automatically upgrade to Windows 10). I found the way to stop automatic upgrade of Windows (Vista) and then deleted the files that were being "staged" for the update. Unfortunately, it's been about two weeks since I did that, and I don't recall either the exact command / steps to disable the automatic update, nor do I remember where those files were stored.
