Is it possible to perform a factory reset on an old Apple iMac (OS X Snow Leopard) without a disk
Erasing an old 'spinning rust' Hard Drive is not the safest or most secure way to totally prevent data recovery by a bad actor, even if you use the old 'secure erase' functions.

The simplest &amp; most secure method is to destroy it.
Whether that's by drilling holes through it or taking a very large hammer to it is pretty much dependant on how much fun you may find either option ;)

The remains are recyclable no matter which way you do it.