PCWorld: Overclock at your own risk: Intel axes its overclocking warranty.
[1]https://www.pcworld.com/article/3609834/overclock-at-your-own-risk-intel-axes
-its-overclocking-warranty.html

   Jim Bell's note:

   I over-clocked a Z-80B (6 MHz spec) to 12 MHz in 1978, cooling it with
   a thermoelectric device.

References

   1. https://www.pcworld.com/article/3609834/overclock-at-your-own-risk-intel-axes-its-overclocking-warranty.html