I find our Windows 98 PC starts getting very slow and unreliable (eg. sometimes crashing immediately on startup or logon) after a couple of years. A format and reinstall sorts it out, but does take a few weeks to get everything back to normal (since I have other things to do as well!) I think that was a common problem with Win9x, and at that time I frequently heard advice to reinstall Windows frequently - perhaps the advice roro has heard dates from then? I certainly knew people who would reinstall those OSs every 6 months or so. On the other hand, my Windows 2000 laptop went for 4 years without needing a reinstall (would probably have gone much longer if the hardware hadn’t died). I think versions later than Win9x have been more stable, so don’t actually need such frequent reinstalls.