Flash storage requires high voltage to do an erase (which needs to precede a write operation). Back in the EPROM days, that was easy, just don’t supply 25V or

Flash storage requires high voltage to do an erase (which needs to precede a write operation). Back in the EPROM days, that was easy, just don’t supply 25V or whatever. Modern flash still needs those high voltages but generates it on-chip via charge pumps. If your read-only switch physically disconnected the charge pumps, you would have read-only flash.