On Sat, 03 Nov 2012 09:34:25 +0000, Orchid Win7 v1 wrote:

>>> 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.

https://en.wikipedia.org/wiki/Protected_mode

Drivers run in ring 0.  If you access a driver, you can access hardware 
directly in real mode.  Protected mode has to do primarily with 
preventing programs from accessing each others' memory.

> 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... :-(

True.

Jim

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