Thinking out of the box makes every thing possible.
Take for instance what if the OS is not stored or installed in the Hard Disk but comes as ROM chips the WORM type. ie can't be modified hence can't be corrupted.
If there are hot swappable chip slots then redundancy and multi boot OS can be created in a jiffy by just slipping in the chips to the slot. No chance of corrupting of OS.
Also just change from which slot you want to boot at the time of booting or shutting down and hey you have a multi boot PC.
To build redundancy in the PC put two chips of the same Os in the stwo slots and hey if one chip fails the other takes over, I mean high avialability in the data center would never be a problem again.