(Or "power glitch") A sudden increase (spike) or decrease (drop-out) in the mains electricity supply. These can cause crashes and even permanent damage to computers. Computers and other electronic equipment should really include some kind of over-voltage protection in its mains input to prevent such damamge.
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Nearby terms: power cycle « powerdomain « PowerFuL « power hit » Power Mac » Power Macintosh » power-on reset