Posted September 24, 2016

The original design for the 4 levels was purely security and kernel/OS protection. Drivers can't crash the kernel, the programs can't crash the drivers, etc. If something crashes then it's localized. However with the blue screen of death, we see often how a messup either with the OS or drivers which can bring the whole system down. And with Video drivers being pushed weekly with updates, one of the updates by NVidia brought down a lot of computers. At worst it should have shut down the drivers, restarted them, if they crashed again boot up generic reserved VGA drivers.
Actually I'm reminded of using experimental drivers to use a wireless ethernet controller, and when the USB device got unplugged with the laptop, the entire system crashed. This was using linux of course :P
But yes, 3 levels does sound optimal, it's just rarely used.