How to factory reset a late 2015 iMac Retina 5K 27 inch when 'Erase' function is greyed out?

I want to reset my late 2015 iMac Retina 5K 27 inch. Ihave already transferred all my data to a new Mac mini.

I followed the instruction, of which there appeared to be many, to erase my HD but the 'Erase' function was greyed out. What am I doing wrong?



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Earlier displays & monitors

Posted on Mar 23, 2025 7:57 AM

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Mar 23, 2025 9:52 AM in response to Adjes

The "Erase All Contents and Settings" feature is only available on


It takes advantage of the fact that those Macs encrypt and decrypt the contents of their internal SSDs in real time. The "erase" largely consists of telling the T2 or Apple Silicon chip to forget current encryption keys in favor of new ones – which effectively turns existing data on the SSD into so much non-decodable hash.


Your iMac predates the introduction of the T2 security chip by several years, so if you want to erase your drive, you have to do it the old-fashioned way.


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How to factory reset a late 2015 iMac Retina 5K 27 inch when 'Erase' function is greyed out?

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