I happen to own several old laptops, now about 10 years old, that had the misfortune of being delivered with a Windows Vista license and matching Windows Vista OEM installations on their recovery partitions/media. About a year ago, I noticed that updating Vista no longer worked. That is to say, trying to look for updates just took for ever and ever, eating CPU cycles but never coming up with any result. Nothing happened overnight, nothing happened after two or three days, Windows Update just kept wasting CPU cycles.
This problem started sometime in early 2017, and only affected Vista SP2. It was perfectly possible to update a Vista installation to SP1 and then SP2 through Windows Update, but not to the latest state, it would just get stuck. The same problem was visible on three laptops and in several VMs.
Over a month ago I decided to see what would happen if I just left one of those old laptops running. It was a circa 2008 Compaq Presario V3000 with an AMD Turion 64 X2 processor. I booted it up and left it chugging along in the basement. Every few days I’d check on it and the CPU fans were still spinning, with Windows Update keeping one CPU core more or less fully loaded. Then I went on vacation for over a week, and when I came back, the fans were still spinning, and Windows Update was still busy.
Then one day I checked on the laptop and it was silent. Not dead, just resting. I started wondering what happened and soon enough I discovered that lo and behold, Windows Update in fact installed a number of updates from 2017 and was finally done! And that is why the laptop could finally go to sleep.
I don’t know how long the process actually took, but I estimate that it was about three weeks, give or take a few days (more likely give than take).
Now, a fully updated Windows Vista laptop is only marginally more useful than one which keeps wasting CPU cycles by checking for updates. The experiment was however useful in highlighting that a) Windows Update is (or at least was) seriously out of control, and that b) even if it took several weeks, the update process eventually did finish, as surprising as that was.
This is a good example of software which is functional yet its performance is so awful that it might as well be completely broken. With no progress indication whatsoever, after a day or two users have absolutely no reason to expect that the update process might ever successfully complete and give up.