Dualbus, where art thou? (G800 related)

[Amber_Method]

In every rumour I have seen about the G800, the DualBus architecture has yet to be mentioned, despite the fact that in every rumour I've seen, the listed amount of bandwidth is not sufficient to supply the G800s fill-rate. I mean 200Mhz 128-bit DDR is good, but it isn't enough to fill 1800 texels, especially at 32-bit.
Does anyone have any theories on this? I mean , if people were just making up specs, then I think they would probably include the Dualbus, seeing as it has been on every Matrox card since the G200.

Is there some technical reason the Dualbus wouldn't work in that configuration?
We know that Matrox has utilized the Dualbus architecture in the following configurations:
64-bit, SDR (G200)
128-bit, SDR (G400)
64-bit DDR (G450)

Is there some constraint on current DDR memory that says it can't do Dualbus at 128-bit?

I could write a whole bunch of other stuff on why Matrox needs the dual-bus, but I just want any info I can get here.

[Ali]

You are talking about the memory bus, thats external to the Gxx chip. I think the dualbus is the internal bus of the chip. Ie the bus from the core to the registers and buffers etc.

Look up the specs on the G200 and you will see that it did have a 128bit dual bus, same with the G450.

Ali

[Amber_Method]

Internal bus doesn't matter, as the Geforce has a 256-bit internal bus, but it still suffers from having a 128-bit memory bus giving it a bandwidth of 2.7 gigs. The G400 MAX has a bandwidth of 5.312 gigs, so it can do almost hit-free 32-bit color. The Dualbus is a memory bus architecture.

[Ali]

where did you get that 5.312gig bandwidth from?

The G400 has a 128bit dualbus which can act like a single 256bit bus (aka Geforce), but has the advantage of being able to write at 128bits/clock, and read at 128bits/clock at the same time. Or if it needs to, it can read at 256bit/clock, or write at 256bit/clock, but not both at the same time.

Go check the specs at the matrox site, and see what they say.

Ali

[Amber_Method]

Damn, you're right. I know I've seen the 5.312 number somewhere, but it must have been referring to internal bandwidth. Thanks for correcting me before I made more of an ass of myself. Ok, this topic is moot, except that Matrox had better have some way to support all that fill-rate.

[Ali]

Matrox have always been smart. If ATI can come up with Z buffer compression, you can bet that Matrox can do it better.

Nvidia is talking about hidden surface removal, and if they can think of it, then Matrox has probably already done it.

Im sure Matrox hasnt been sitting around all this time since the G400 doing nothing. The G450 probably took very little R&D time, most likely they were waiting for the .18 fab to be ready to take it.

My guess is that MAtrox had a long hard look at the rendering process after they got the G400 out. They would have guessed at the fastest speed ram that would be out there by the time they wanted to release the G800, and what fill rate they wanted to have.

They I guess they would have looked at ways to reduce the bandwidth thats used. This includes Z-buffer compression, Clipping, Texture compression, etc.

Another way is to go to tile rendering, and Im guessing that the Condor will be Matroxs first Tile rendering chipset.

Matrox have smart people working for them, Im sure they will have designed a good, balanced card.

Ali

[Nuno]

G400 doesn´t have a 128 bit dual memory bus. Period. You wish! That dual bus thing refers to the G400 chip itself, NOT the memory interface.
There is no such thing a 128 bit dual-bus (two 128 pathways to memory) That would require too many pin conections on the graphic chip and too many PCB traces. Very unpractical and expensive thing to do. There is no such thing (yet?) as a 256bit memory interface for video cards. An elegant turn around is DDR memory, that effectivly doubles the memory speed, but it´s STILL a 128 bit bus.

[Ali]

I think we had already sorted that out

[Nuno]

Ooops, sorry, you´re right, but for some strange reason I only got the 1st post displayed...

[Himself]

G200 had 64 bit dual bus, the 128 bit dual bus was the G400 addition. It doesn't matter how much internal bandwidth a chip has, if it uses the same ram hardware as the rest it will have the same limitations as the rest.