Kulwinder Atwal wrote:
> 
> AGP is meant to allow a card to use system memory, instead of having to
> add more memory to the card.  AGP allows the card's processor (ie. video
> processor) to bypass the CPU and directly access main memory.  This
> allows a CPU to do more important things with its time.
> 

I don't think that's really right, cause the usage of memory directly
from PCI is available too.
It's called bus-master transfert ( from or to the PCI-card ), and this
operation is done without main CPU.

The first advantage of AGP bus is that this one can be considered as 'a
second' PCI bus with only one peripheral ( this explain the full
bandwith operation for one slot ) and the frequency of the bus which is
66MHz against 33MHz for the PCI.

This point of view explain why there is only one AGP bus on the system.
( if you look at linux /proc/pci file info, you will see that the AGP
card is considered as a PCI card on bus=1 while others cards are all on
bus=0 )

Chris.

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Kumsta Christophe
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Real-Time System developper
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