The slow corruption of stored data by nothing in particular. It was fine when you left it. Leaving it was the problem.
The plate is not being attacked. It is being stored. Storage is the attack — media sheds charge, rays flip cells, the word drifts toward noise one bit at a time. SCRUB rewrites it from the checksum record and buys you a clean plate that starts rotting immediately. ECC catches most flips as they land and never all of them. There is no third button. There is no state called safe — only watched.
Rot is one of the oldest verbs in the language because decay is one of the oldest observations. For a thousand years it applied to things that were alive once. The bit had to be invented before it could start rotting.
Magnetic tape sheds oxide. Drum memory drifts. Early operators learn that a stored bit is a wager against physics, re-spooling tapes on a schedule like turning cheese in a cellar. Storage is not a state; it is an activity.
The Jargon File records the joke that programs decay while nobody touches them — bit rot, software rot. The punchline is that it is not a joke. Formats drift, dependencies vanish, assumptions expire. Untouched code stops working, and untouched data quietly stops being data.
IBM studies confirm that radiation — trace isotopes in chip packaging, particles from space — flips DRAM cells at measurable rates. ECC memory ships: extra bits standing guard over the real ones. The failure is now physics, priced per megabyte.
Silent corruption gets a name and a hunting license. ZFS checksums every block end to end and scrubs pools on a schedule — reading data for no reason except to see if it is still true. The Keeper's liturgy, automated.
The BBC's Domesday Project stored a nation's self-portrait on laserdiscs that were nearly unreadable within twenty years, while the parchment original it honored remained legible after nine hundred. Librarians coin 'digital dark age' and mean it. Link rot eats a quarter of the web's citations.
Every archive that survives, survives because something keeps walking the shelves — scrubbing, migrating, re-encoding, checking sums against the slow fire. Bit rot is the honest name for the default outcome. The word never fell out of use because the problem never fell out of existence.