We sat down with David "Tabasco" Nalasco from ATI during their R520 launch in Ibiza. David was resposible for the CrossFire section of the presentation which is what we casually talked about.

Why is the current X850 CrossFire limited to 1600x1200 resolution at low refresh rates- would a better chip used for compositing engine helped?

The limitation is due to the DVI link because DVI has a certain amount of bandwidth which is at 165MHz x 8-bit. There’s a certain amount of bandwidth there and we wanna use that bandwidth to communicate between the two cards. (Since) one card is not opened for display so we can use all of that bandwidth dedicated to pair those (cards).

The actual speed of the PCI Express bus is faster but first of all, that’s peak speed. Real, actual usable bandwidth is less and its also being shared for communication with the chip. Those were our two options (and) we actually got more bandwidth by dedicating a DVI link but (again) the DVI link has a limited amount of bandwidth to those certain resolutions regardless of what compositing engine we would’ve put on the master card to get the data to the slave card at a certain rate so that’s where the resolution limitiation (kicks in).

So how did this problem get solved with the x1800 series- aren’t you’re using the same type of connectors?

We have integrated a dual link DVI on all x1000 series cards and that gives us more than enough bandwidth (for) the highest resolution displays which is 330MHz so you can handle resolutions like 2048x1536 at over 70Hz analog or digital. Not sure what the highest resolution is but we can drive the 31” Apple display. There’s really not anything interesting for the consumer level higher than that at the moment. That worked out quite well and we support that with all of the chips. In fact on the x1600 and x1800 we have two dual link DVI ports (while the) x1300 only has one (dual link) and one single link to make (it) low cost.

So for these new R520s, is the composite engine built on the chip or is it still a separate chip.

No its still a separate chip

How come you made that decision?

The compositing engine is really only necessary on a master board. Its only necessary if you want to use CrossFire. Other wise you have additional costs associated which would have to be on all the chips whether or not you’re interested in CrossFire. The fact is that percentage of people that will use a CrossFire solution is very very small.

So basically this was something that increases the costs and you didn’t want that.

Yeah. Going forward, we may be integrating some of the stuff but for this generation- its still very new technology.