why panic(9) ?

Nils Holland nh at tisys.org
Wed Jan 12 13:13:45 UTC 2011

C. P. Ghost wrote:

> As far as I know, Windows NT is a microkernel arch, and
> faulty drivers, often provided by external vendors would not
> bring that system (as much as we hate or despise its
> Windows OS personality that runs on top of it) to a complete halt.

I don't know ... when Windows crashes (I'm no fan of it either, but anyway) 
and you ask Microsoft about it, then it's most of the time an external 
driver that is responsible. Graphics card driver seem to be the cause most 
often, but other stuff as well. Here at work, we had a Windows Vista (moving 
the focus of this discussion away from Windows 2000) machine that crashed 
every time it was attempted to establisch a PPTP VPN connection. The reason, 
as the blue screen clearly showed, was a faulty driver that was part of a 
firewall made by AVG.

So I would vote for exactly the contrary: Windows itself, in terms of "just 
the Microsoft components" is fairly stable, and it's third-party drivers 
that tend to bring it down most of the time. Having a job in which I have to 
support people working on Windows, I can say for sure that there's no such 
thing in Windows that prevents third-party system level stuff to bring down 
the system. ;-)

But back to the topic itself: Of course panics are useful. It's not a 
feature you'll use to advertise your operating system with, but an 
appropriate comparison is this: When you no longer know what you're doing, 
it's better to just stop immediately. And that's what a panic does: When the 
kernel has somehow gotten into an "undefined" state it cannot cope with, it 
just pulls the plug before any additional damage can be done. Totally sane 
thing. Of course, improving the kernel so that such "undefined states it 
cannot cope with" occur as little frequently as possible makes sense (and 
FreeBSD is certainly very good in that area), just "removing" panic doesn't 
make any sense. When somehow you've gotten in front of a tunnel and there's 
a train approaching, you don't believe that just standing still and closing 
your eyes will save you. ;-)


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