10 YEARS, thank you very much.
First: Pentium II. It booted Win95 when it first came to life, and ended up with XP SP2. I can still remember it had 394MB of RAM, and it came with 64MB only. Only formatted 3 times, including the upgrade to Win 98 and Win XP. And I played all games possible on it, thank you. 10 years chugging happily. The PSU on it had a fan that died, but easily replaced. The thermal paste evaporated after 8 years below the tiny fan on the slot, but it didn´t die. Sold it in perfect working order.
Second: Pentium IV. This mean old codger booted Win 95, Win 98, I regret to say Win Me, and Win XP. As with the others, it begun with 256MB and ended with 3GB, topping out the mobo. Suffered one lightning bolt strike, that fried onboard sound and network (the lightning came through a video capture card that fried a VCR and a TV), but it still works. Yes, I own it.
But the champion is an IBM Aptiva Pentium I. This crusty old geezer, that I owned before the PII, was donated to charity, and later, as in 15 years later, I visited the place where it was STILL RUNNING. Passive Cooling has got to do anything with it. Yup, no fans, the only loud noise was the 4GB HDD, upgraded from the borked 1.2GB that came in it.
Most of my machines lasted 10 years, one lasted appaling 15 and still going. My next one will last another 10, I hope so. Saved me tons of money. I usually skip 3-4 Moore's Law generation, each time.