Question about dual monitors

[Daniel Carrera]

Karl Auer wrote:
>>How is X.org or Xinerama supposed to know which one is supposed to be 
>>the LCD screen on my laptop and which one is the CRT connected to the 
>>VGA output?
> 
> Because in the screen section you say what monitor to use and what
> device it is attached to. A screen is a monitor attached to a device.
> And in the device section you number the screens.

This just shifts the question to the devices. Given that in reality 
there is only one device in the PCI bus, how does X know which one is 
supposed to be the external monitor. Here is another snip from the 
config file:

Section "Device"
         Screen          0
         Identifier      "Intel Corporation ..."
         Driver          "i810"
         BusID           "PCI:0:2:0"
EndSection

Section "Device"
         Screen          1
         Identifier      "Intel Corporation ..."
         Driver          "i810"
         BusID           "PCI:0:2:0"
EndSection


Notice that the devices have the same BusID and identifier. What is to 
tell X that Screen 1 is supposed to mean "VGA out"? The same is true for 
your config file. Let's take a look at what you posted:

> Section "Device"
> 	Identifier	"ATI_0"
> 	Driver		"radeon"
> 	BusID		"PCI:1:0:0"
> 	Screen		0
> EndSection
> 
> Section "Device"
> 	Identifier	"ATI_1"
> 	Driver		"radeon"
> 	BusID		"PCI:1:0:0"
> 	Screen		1
> EndSection

You see that those are actually the same device? Okay, you've chosen 
different identifiers. But the identifier is just a user-chosen string. 
There is nothing to tell X that "ATI_1" means "VGA out". These two 
devices are the same.

Cheers,
Daniel.
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