telford <[EMAIL PROTECTED]> wrote: > If you do not want to go the whole hog and run a fully isolated virtual > machine then you MIGHT be able to recover SOME of the time but think about > a situation where you have swap-to-disk implemented as a user space task > and it crashes. Can you recover the situation? All memory on the entire > system is now in an untrustworthy state so you must find a way of cleanly > restarting every task -- most people call this a reboot.
The point of a microkernel is that for the swap to become corrupted, the swap service must be buggy. It doesn't matter to the swap system how buggy the graphics or network drivers are, for example. Different tasks can even be using different virtual memory systems, so if one crashes then processes using the others are completely unaffected. > And because microkernel designs have been tried (e.g. MS-Windows NT) > and so far they have proven both slower and less stable. NT was never released as a microkernel, although that was the original plan. It has only ever pretended. NT's instability is mostly due to shoddy graphics and other drivers being loaded in kernel memory for performance reasons. In other words, the instability is due to *failing* to really be a microkernel. QNX was the first microkernel to demonstrate decent performance, and that came at the cost of flexibility and performance. More recent research has lead to more portable and flexible microkernels with high performace such as L4. When Linux first came into existence, microkernels were still just a neat idea with a few big problems and were a long way from being proven. The high cost of context switches and switching supervisor mode (ring zero) on and off on x86 makes things difficult for any microkernel. -- Sam "Eddie" Couter | mailto:[EMAIL PROTECTED] Debian Developer | mailto:[EMAIL PROTECTED] | jabber:[EMAIL PROTECTED] OpenPGP fingerprint: A46B 9BB5 3148 7BEA 1F05 5BD5 8530 03AE DE89 C75C
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