Re: More layers as VAX/VMS
Well this wasn't true in VAX days - drivers ran in the kernel ring, though less critical parts were sometimes farmed of to a user-space process (ACP). As I recall, parts of the filesystem ran in Executive mode and the DCL shell ran mostly in Supervisor mode.
Post-VAX, some of these modes are virtualised as the CPU architecture doesn't support all the necessary modes, or, as in the case of the x86/x64 implementations, only the innermost and outermost modes function efficiently.
There's certainly an argument that modern requirements (where you have lots of third party software, much of it running from unknown sources on the Internet, often unbidden) would be easier to serve with either more protection rings - or a less hierarchical model with better compartmentalisation - but four rather than two is not going to make much of a difference.
Biting the hand that feeds IT
