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Apple’s Photo Bug Exposes the Myth of ‘Deleted’
(www.wired.com)
This is a most excellent place for technology news and articles.
Rewriting bits to 1s or 0s is very slow especially in mechanical drives and is hard on equipment. Even SSDs have a rated max writes, if we rewrite all data every delete it will decrease the lifespan of hardware.
This is why is assumed they mark them to overwrite. Google knows a lot about what makes drives last longer, and OS and drive firmware makers have known for decades too.