How does bitrot work?
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Bitrot is a general term for memory cells in a storage medium breaking from wear and tear.
The actual reasons can be very diverse, dust, heat, EM radiation and so on.
When that happens a memory cells content isn’t reliably correct anymore, for example the cell can be locked into 0 despite having been written a 1 before.
This happens quite rarely, but when it happens it can be catastrophic depending on what was saved there. Therefore techniques are used to recognize broken cells and rewrite the data into an intact cell instead. One way to do that are checksums. Every X cells your write their digital sum so if some cell is incorrect the sum doesn’t fit anymore you can immediately see something is wrong in this section.
It totally depends on the medium, but either the medium itself degrades over time, or the phenomenon holding the bit (magnetic/charge) decays over time. Most storage mediums and drive formats have error correction so can tolerate a certain number of erroneous bits – but once a threshold is reached then data errors occur.
For something like a pressed CD (non writeable), oxygen from the air diffuses between the layers – particularly at the edges and slowly damages the bits.
For a magnetic hard drive, magnetic fields decay slowly over time.
For a charge based flash drive, the charge can gradually leak out.
Then you get things like cosmic rays which can flip a few bits if they hit a storage medium. Over time this can build up to cause issues.
“Bitrot” just means that data storage gets corrupted over time. Anything could be the cause. Sometimes the materials themselves just degrade over time because of UV radiation, heat, humidity, oxidation, or physical wear. Sometimes, the property that makes it able act as storage degrades with time — magnetic fields flip a magnetic state, a stray bit of radiation flips a gate, whatever.
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