I always found it interesting how much Intel's protection ring architecture dictated the direction of operating systems back in the 1980s. (I'm sure Intel didn't even invent it; similar concepts were probably already in place in mainframes?)
x86 has highly specific support for protection rings and switching between them, as well as things like page faulting and interrupt management, leading to the classic kernel/user split with a kernel as a privileged actor underneath a user mode.
But having just one exclusive, reserved "kernel mode" is starting to look old, which is why there's now so much talk about virtualization and exokernels and so on. The microkernel design certainly seems very elegant, but it looks to me like Intel's architecture was always a stumbling block. You have to wonder about what hardware support you could invent that would make microkernels a better fit.
x86 has highly specific support for protection rings and switching between them, as well as things like page faulting and interrupt management, leading to the classic kernel/user split with a kernel as a privileged actor underneath a user mode.
But having just one exclusive, reserved "kernel mode" is starting to look old, which is why there's now so much talk about virtualization and exokernels and so on. The microkernel design certainly seems very elegant, but it looks to me like Intel's architecture was always a stumbling block. You have to wonder about what hardware support you could invent that would make microkernels a better fit.