>> Surely you can't actually do that in a protected-mode operating system.
>> (I.e., anything less ancient than Windows NT, circa 1993.)
>
> Protected mode operating systems don't have anything to do with
> preventing I/O operations from happening....

Yes it does.

It means your program can't just casually access the underlying hardware 
directly. It has to convince the OS to do that for you. (Or install 
itself as a device driver - which again requires convincing the OS.)

So, yes, if it's a protected mode OS, you can't just hit the metal 
directly. Whether the OS will refuse to do the operation on your behalf 
is still up for debate, however... :-(

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