General question about modern GPU's

[pigdos]

Are modern GPU's dual-ported? By this I mean do they have separate data
busses to handle the on-board, local video memory and read data off of the
AGP or PCIe bus? If so, can a modern GPU be reading data off of the AGP or
PCIe bus AND simultaneously be writing/reading data to the on-board, local
video memory?

If the above is all true then I would figure overclocked video cards may be
bottlenecked by the AGP bus. Assuming the GPU has a 4-byte wide interface to
the AGP bus and is running at 580Mhz (like my X850XT) wouldn't its
theoretical bandwidth be more than AGP 8x? AGP 8x xfers 4-bytes at 533Mhz so
that would be less than the theoretical bandwidth of my X850XT (4-bytes @
580Mhz).

 

[Acid8000]

Are modern GPU's dual-ported? By this I mean do they have separate data
busses to handle the on-board, local video memory and read data off of the
AGP or PCIe bus? If so, can a modern GPU be reading data off of the AGP or
PCIe bus AND simultaneously be writing/reading data to the on-board, local
video memory?

If the above is all true then I would figure overclocked video cards may be
bottlenecked by the AGP bus. Assuming the GPU has a 4-byte wide interface to
the AGP bus and is running at 580Mhz (like my X850XT) wouldn't its
theoretical bandwidth be more than AGP 8x? AGP 8x xfers 4-bytes at 533Mhz so
that would be less than the theoretical bandwidth of my X850XT (4-bytes @
580Mhz).

I'd imagine they're separate. If you use an application such as Everest
Home/Personal Edition (now discontinued), it reports the GPU to video
RAM bandwidth. As such I interpret this as indicating independence
between the AGP and video RAM bandwidth.

-Phil