Jon Forrest wrote: > Geoff Jacobs wrote: > >> Everybody take a moment to remember how Windows NT was supposed to be an >> elegant, microkernel design. > > At one point, in its early history, NT was a microkernel design. > However, since hardware was much slower back then, Microsoft > decided to break down and put some things, like graphics, that > were initially in user-mode "servers" into the kernel. > > There were some people who objected to this, saying that the > original pure design resulted in a more reliable OS, since > user-mode bugs couldn't crash the kernel. However, the pragmatists > pointed out thohat many of these user-mode servers were so critical > to the running of the OS that if a user-mode server died, then > OS became unusable anyway, so what was the point in staying > faithful to the microkernel mantra. > > Of course, these days hardware is so fast that microkernels > and VM hypervisors don't add enough overhead for most people > to notice. > > Cordially,
Until NT4, most critical processes ran in user land. Microsoft did with NT4 what Apple did with Mach -- move much of the critical system processes, including graphics, into the kernel to boost performance (as you said). I never ran NT 3.5 back in the day, so I don't know what the reliability numbers are like, but I can't imagine it could be worse than the early service packs of NT4. Assuming that code quality is similar, NT 3.5 should have been quite a bit more resilient than NT4, but I just don't remember. Certainly, QNX provides a good example of how reliable a microkernel OS can be. Anyway, anyone have examples? Now, why did Apple go the same route. They essentially wrote an obsolete operating system with Mac OS X. Why didn't they go microkernel? Of course, Mach is a pretty horrible kernel to start with and was likely only used because of the NextStep legacy. It basically wipes out any performance gains from their high level of integration, but I guess they didn't want to devote the resources to going fresh with something like L4. -- Geoffrey D. Jacobs To have no errors would be life without meaning No struggle, no joy _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
