Why does Windows' performance degrade over time even when it isn't used?

Question

I know that similar questions have been asked before (like this and this), but none of them answer my question. My problem is, as stated in the title, that when Windows isn't in use (some months) its performance degrades. (Boot time goes from ½ minute to 2 minutes) If I boot Windows every day for a week, the boot time shrinks, but I have disabled defragmentation.

The other answers indicate that it might be fragmentation or bit rot. I know for sure that i can't be fragmentation since the hard drive is not use when not booting Windows (except for benchmarking from Linux). However, when benchmarking the drive under Linux (always booting from a separate drive), the drive's performance doesn't drop over time.

Edit: The computer I described in the question runs Windows 8, however I've also experienced this on Windows 7.

Answer 1

Windows uses something called prefetch which is basically a cache of the process you use the most. If it were to expire, Windows would have to build it from scratch again.

I personally haven't experienced something like this, I use Windows roughtly once every month and it takes the same time to boot always and the performance once it's loaded is the same (it's Windows 8.1 though, I don't exactly know the inner workings of it or prefetch).