Hi Dean,

Having not only built computers, but written device drivers for Windows as
well, I can answer what a Blue Screen Of Death (or BSOD) means.

It is basically what happens when the OS detects a problem that it cannot
deal with. Typically, an application level problem (which runs at a
processor or IRQ level called "passive" level) can be detected and
gracefully dealt with (even to the point of just terminating the program).

However, device drivers, and the core OS run at more privileged levels like
displatch, interrupt, and device levels. Since most of the core OS services
also run at these higher levels, a fault that is detected cannot be handled
so the OS basically drops to a very simple fault handler, and writes the
basic error code and information to the screen. Since even the video driver
is no longer in a valid state, it assume the most basic VGA mode of the
video card and writes a simple text message using the most basic services
available.

A typical example is an attempt by a driver to access a page of memory that
is not locked down. Since the memory manager is not available at these
privileged processor levels to page the memory in, it cannot continue, so
you get a BSOD. This is just one of the more common BSOD faults, there are
quite a few. Writing code for device drivers takes a whole separate level of
training than for applications.

Russ Poffenberger

-----Original Message-----
From: PCBUILD - Personal Computer Hardware discussion List
[mailto:[log in to unmask]] On Behalf Of Dean Kukral
Sent: Sunday, January 01, 2006 12:56 PM
To: [log in to unmask]
Subject: [PCBUILD] Why is it a BLUE screen of death?


I was reading Peter's question about a possible failing video card, and it
got me wondering:  Why is it a
**blue** screen of death when your computer crashes?

I have had black screens - that makes sense.  (SP2 caused them.)

But why Blue?  It seems that if the computer crashes, then garbage should be
going to the video card and GIGO!

Do video cards put out a blue screen by default when the input directions
make no sense?  Then, a blue screen would seem to make the video card less
of a likely culprit when there is a system crash, as it is doing what it is
supposed to be doing.

Dean Kukral

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