What is TRIM on an SSD?
In one sentence: A message a computer sends to an SSD saying which blocks are free, so the drive can erase them in the background.
A little more
Flash storage (SSDs, phones, memory cards) can't simply write over old data; it has to erase blocks first. TRIM is a message the computer sends saying "these blocks are free now", so the drive can wipe them in the background and be ready for new data.
A side effect is that deleted files on SSDs often become impossible to recover within minutes, unlike on old spinning hard drives.
It's a bit like… Telling the cleaner which desks are empty so they can wipe them overnight.
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